Seems like no one advertises Shimano cogs on line.
Does anyone know where I can get Ultegra 10 speed replacement cogs (CS-6700)?

Cogs as in cassette cogs or do you refer to chainwheels? Shimano does not sell cassette cogs separately.
Chainwheels are available "everywhere".

Well, yes. Cassette cogs.
That's news to me. Why would they even be replaceable then?

Who said they are replaceable?
Just because some of us swap them around, that doesn't exist in Shimano's mind.
Miche makes cogs if you want to pay a primo price/cog.

Look under CS-6700, EV-(exploded view) SHIMANO Dealer's Manual / User's Manual Get the part number and use to do a search. Miche cogs can work but are a different thickness at the base combined with a slight offset so spacing can be a challenge if inserting between Shimano cogs.

Yep, did that:

Y1Z81400D
Y1Z81500D
Y1YX1700D
Y1YX1900D
Y1YF21100

Got nothing in English except pdf's.

I guess by "replaceable" I meant why even have separate part numbers. Call me old school (which I am) but I remember the days of freewheels when you could get replacement cogs.

They have separate part#'s because cogs are specific to "speed" & tooth counts of adjacent cogs.
Hyper Glide!

It sickens me a bit to think that just because a couple cogs in the middle of the block are getting worn I should change the whole bloody thing.

Shimano Ultegra CS-6700 10-Speed Cassette Not like the entire cassette is expensive. What would you hope to pay for several cogs? I'll make a WAG that a cassette will last you several years....

Everyone's different but I never thought a cassette was that expensive of a consumable. Maybe I'm just rich.

Just buy a new 105 or Tiagra cassette. Cheap and there's not much difference between them and Ultegra, maybe a tiny bit of weight and visual finishing of cogs.

I'm with you on this one.
"Back when" we had a cog board w/ all of the individual cogs and spacers to build a custom FW or simply replace a worn single cog for Sun Tour and Shimano.
Small cogs wear faster than large one making an entire FW/cassette replacement necessary when one 15T would keep it in service for another season or two easily and inexpensively.

Those days are gone.
It's part of the disposable parts-changing mentality where sets of cassette cogs are pre-pinned to keep parts from being installed upside down or spaced wrong in the tight tolerance of indexed systems. Worn 15T? New cassette time.
Lawyers & inventory control experts at work.

-Bandera

I bought a couple of 6600 single cogs online only a little over a year ago and now they are nowhere to be found. ChuckD641 have you tried calling some bike shops? Some shops are more willing to look into ordering these parts than others so try a few of them. Possibly Shimano may just be discontinuing selling singles. "Just buy a new cassette", Ahhh, the throwaway world, what a waste.

Yeah, it's not like it's gonna break my bank account, it's more about adding to the waste stream (have you kids noticed the landfills lately?) or adding to my parts pile that I keep thinking will be useful someday but so far hasn't been.
I did shoot email to Niagara who've been helpful in the past but got a machine response back saying basically answering wasn't their highest priority. I'll call around here though too.
'Ride a single speed'
brilliant. funny stuff.

How many "cog boards would be required now?
I doubt your local LBS would be interested in taking up that much space to sell a couple cogs/year, when you can get complete cassettes with ALL new cogs for cheap.

There's a part number on the EV for individual cogs, but I have never heard of anybody really stocking them. At least not in the US.

Like I said: Those days are Gone.
Your LBS can't decide whether it's worth the inventory investment to own a 6700 & 6800 cog board since neither exist.

-Bandera

Since one cannot reliably judge cog wear by sight, I guess you've installed a new chain and found that it skips on the couple of cogs you want to replace. How worn was the chain you replaced? If you let it go too long, other cogs may be compromised as well. Two chains per cassette seems normal.

A reasonable question. For one, this cassette has around 3K miles on it. Yes I did install a new chain and have been swapping a couple in over time. No, it doesn't skip but shifting on those middle cogs is sluggish.
And I also own the Rohloff tool for determining cog wear and that tells me they're approaching end-of-life.

A lot of individual sprockets are up on E-Bay.

Shimano has been trying to limit the online sales of their products, perhaps to the harm of the consumers. But, you could take your part numbers to your local bike shop and they may be able to order them.

However, as mentioned above, say you spend $10 per sprocket, plus shipping, it won't take long to spend more than the price of a new cassette.

I got some 17/19, 9s sprocket sets from CambriaBike.com a year ago. I'm not seeing more on their web page, but you can contact them.

If you have a big trip or race planned, throw on a new cassette. Otherwise, ride the old one until it goes bad. Perhaps pick up a good "spare".

Cool tool!! Does seem like very low mileage out of the cassette, bummer.

Yeah, the cogs all have individual part #s so that Shimano can keep them straight internally, not to facilitate sales to us...

As I mentioned, this isn't about cost saving, altho if it goes much over US$50 I'll spring for a new cassette. It was simply a question if anyone knew of a source for cogs. I would much rather keep a perfectly good cassette body out of the garbage or my spare parts heap, if I could.
Thanks all for the feedback.

Cassette body?
What's that?
You can separate cogs and throw them into the scrap metal bin.

The Ultegra cassettes at Nashbar are under $40. Save yourself some money....