There is a guy that quite often advertises on Ebay and has kits for more cameras than you can think of, he is out of Florida and seems to advertise for Kievs most of the time.
If your Yashica is a TLR then I recommend Mark Hama very highly. He is in Marietta Georgia and did a terrific job rescuing my 124 from a colony of Hawaiian ants that were living inside it....
I realize that I should have mentioned that it is 35mm SLR. If you say "Yashica" to me, I automatically think TLR too and I don't even have a 'Mat. I have a couple of Yashica bodies because they take Zeiss lenses.
Mine needs new foam in the channels, at the hinge and the mirror cushion.
the man on Ebay is called "interslice" he is great and has all sorts of kits and designs for loads of cameras - and excellent help and advice on doing the repairs and includes a special tool for removing old goo and inserting new seals and foams
in case he has no kit for your camera, you could cut your own. Get 0,5mm thick black rubber foam, cut it with a scissor (a knife is no good, the edges are too rough). Remove the old foam with a toothstick, q-tips and a solvent (aceton if no plastics are involded, isopropyl alc in that case) and fix the new stuff with a bit of rubber cement.
I used that rubber foam with my Kievs, my Olympus 35RC, many others did it to their cameras... works.
Thanks Roman
It appears that interslice doen't sell camera-specific kits, but rather sends you a variety of materials that would be used on any camera. I think that it is up to you to do the final adapting to your make and model.
I would add that I found no need at all to use any glue for the light seals around the film door on my OM10. Only the mirror damper needed adhesive and there was the correct adhesive backed foam in the kit.
I would be quite reluctant to use glue for any light seal replacements unless absolutely necessary.
Mirco Tools, look em up on the web, sells an assorted pack of self stick light baffle (get the USA made for better density) for $20. You cut the strips with a razor. Pick out ALL of the old goo, stick in the new and you have enough left over to start a business. Those kits aren't self stick so you will have to use some contact cement and that is a mess to deal with.
BTW you don't need camera specific foam, you need strips of the correct thickness and lengths.
Interslice's foam for the grooves along the top/bottom aren't self-stick, but they work just fine using what is basically a pressure fit insertion. The other pieces of foam, of varying thickness, are self-stick.