I followed a reference from Bob Fowler's site to this guy who sells foam for light seals and such. His name is Jon Goodman and I emailed him and asked about getting a 4"x4" piece to use with a small packard shutter I got from Jim Galli (it's all connected don't you know). Jon emailed me back just now and is sending me the piece for free. He said he had some left over and it was no big deal.
I think this really is a big deal. Sure it's one piece but any store, online or otherwise would have charged me. Jon didn't have to comp the piece but he did and I wanted others to know about this resource. I'm not saying he's giving everyone free stuff, but if you're looking to do some light seal work you should contact this guy. It was a hell of a first impression.
I agree, MenacingTourist, I bought a light seal kit from him on eBay. It costed nothing and will last forever, an excellent deal. He's also one of the friendliest sellers I've met on eBay.
I bought one kit and completely resealed two Mamiya 645's like the instructions called for. Took them to Paris and had no light leaks. The materials are of the highest quality.
Just to join the Jon-fest... I agree with all the above. He also ships overseas so there's no excuses for anyone to miss out on nice gunge-free light seals...