I am trying to preserve the drivetrain in a dinosaur, but a nice one. Any help on where to find these three hard-to-impossible-to-find items would be greatly appreciated.

Long story:
Soon I will need service my '82 Stan Pike drivetrain. I want to make as minimal change as possible. I currently have a NR 52/42 and a Suntour Perfect 888 with 16/17/19/25/32 - this ratio has served me well for hills and touring since I built the bike up. This gives me a range of 88 to 35 gear inches with the existing 27" wheels, AFAIK.

Most of my riding is on my 19 tooth rear - and now it is almost at 0.5% wear. I've been changing out the 19T (I had 3 spares) when worn. Now, when I pop a new chain on, I have to ride gingerly for a week or so until the chain stretches a bit - obviously, not a great situation. I rarely use the 16 tooth, and occasionally the 17T.
I know that I could remove and replace with a new freewheel and buy and fit a compact crank (once I figure out sensible and available tooth combinations), but this is more change and expense than I want to commit to at this time. I have little space in my rented house, and no workbench or space for it. (I could also buy or build more modern rear wheel, and convert from 27" to 700c, but that means getting some Tektro or other brakes - I'm 3-4mm shy of having clearance, even with a drop bolt. - so I'd like to do as little as possible now. Otherwise, a complete refit is the next logical step, and I'd rather leave this for either when I have a workshop and plenty of time + dollars on my hands, or else leave it for the person who eventually buys the machine when I can no longer ride it.)

What I'd like to do is simply replace the worn 19T not threaded freewheel cog and 17T threaded with unworn ones, (that's all!). The 19T one I need are (I believe) Suntour "A" cogs - not threaded - with four semicircular nubs at 90° to key into lands in the freewheel body. But I'm not 100% sure the cog pattern is identical in the "Perfect" and "Winner" &"New Winner" freewheel models. I'm looking for one that will fit the Perfect model. The 17 is threaded - does anyone have this one to fit Perfect?

Finally, does anyone have or know where I can get an adjustable cup lockring for standard NR British BB? Mine has suffered torn lands - maybe my Sugino wench doesn't fit intimately enough - it has slipped off a few times now and I can't seem to find a replacement lockring - or the next overhaul will be the last with that BB set.

Thanks! BF rules!