I am looking for possiblity to replace cantilever brake on my gravel bike with an easier to deal with mountain brakes. But the only adapter I know to enable this, Problem Solver Travel Agent Bike V Brake Adapter seems to be out of stock everywhere. Any alternatives?

If you are using those link wires I would suggest ditching them for straddle cables and Problem Solvers Wide Cable Carriers instead. Makes it much easier to adjust the canti brakes. Leave the straddle cables as long as possible. You will need to make certain that there is something to catch the cables if the main brake cable parts or comes loose so the wire doesn't foul the tire and lock the brake, but a fender or existing reflector bracket or a piece of cord will suffice.

Or consider short arm linear pull brakes (as short as 75 mm). I haven't seen an installation that looks very good, especially with very narrow rims, but some make it work.

There are also long-pull brake levers available from Tektro and even adjustable levers that can be set for both short and long pull operation.

I assume that you are talking about direct pull (v-) brakes. I don't have much experience with either. My understanding is that the advantages of v-brakes are
1) Gives a nice approximation of center-pull brakes without requiring a fixed mounting point for the cable - useful for bikes with suspension
2) Doesn't protrude from the bike.

Are there other advantages? I haven't much experience with either type of brake.

Ok, let me elaborate:
-I have a "travel bike", ritchey breakaway cross steel frame, 35mm tire wheels, sram double tap shifters/levers. I bought this second hand and use on an extended trips where I will ahve free time to cycle or on some tours.
-with these specs cantilever brakes is what was used to build the bike. However, it could be just me but it takes me about the same tiem to get these adjusted on the reassembly as the rest of the build. I was hoping going for direct pull v-brakes would be idea.
-I went from cantilevers to mini-v brakes on my tandem and the results is good. But with 35mm and possible interest in the fenders - I think I would like to get regular v-brakes here. Not really interesting in upgrading levers etc...
-If there are upgrades to make cantilevers easier to control/adjust - please share the details!

Only place I'm aware of that still has the Travel Agent is SJS Cycles in the UK. I vaguely recall hearing something about how they took over the mfr. of these but not positive about that. Anyways, they have them but not cheap. https://www.sjscycles.co.uk/cables/t...-each/?geoc=US

Wolftooth has the TANPAN, which is built for derailleur incompatibility, but it may also be useful for brake pull problems.

The nice thing about the Travel Agents over other brands is that they were designed to replace the noodle, and thus worked specifically with the V-Brakes.

Wow, they are just disappearing from the marketplace.

How about this one?

https://www.ebay.com/itm/Travel-Agen...s/333290916192

I wonder if Disc brakes have been killing them off. The straight ones were discontinued quite some time ago.

When I put v-brakes on my gravel bike they worked just fine with road levers and an adjustable noodle.

They offer comparable clearance to traditional cantilevers while being (usually) easier setup due to fewer variables, plus no risk of a straddle locking up a tire. It's also easier to avoid judder with V-brakes than many canti setups, since the cable isn't stopped above the steerer. Their simplicity also means that even very cheap models usually work quite well and aren't terribly heavy.

The quirk with v-brakes is that full-size models have incredibly high mechanical advantage. Even with long-pull levers or pull adapters, the mechanical advantage frequently remains very high, not a lot of pad movement for lever pull. So they tend to be sensitive to pad wear, and can require that the wheel be at least reasonably true. But, this also gives them their high braking force.

I love 'em. In dry weather, the set on my gravel bike feels about as good as the hydro discs on my MTB.

As much as I hate it when the Chinese steal American designs, in this case the originator no longer wants to sell them. There are several outfits selling clones on Ebay, in a variety of colors and prices. I have Travel Agents on several bikes and just ordered a set of these. I don't find the Tektro road bike, V-brake levers comfortable as they are too narrow for me.
Road Bike V Brake Adapter Converter

I've known the owner of Problem Solvers (and QBP) for over 40 years and the next time I see him I'll ask why they were dropped. My guess is fear of lawsuits. Or actual lawsuits. For people like us, they aren't tricky to set up, but not everyone is mechanically inclined.

More than likely it was a temporary shortage earlier this year when this thread originated. I just checked QBP and they have them in stock.

Leave the straddle cables as long as possible.

There is this 12/6/2019 blog post.
https://problemsolversbike.com/index...ch-your-brakes