I think the kit I did buy previously was a Jon Goodman one. However, I went to a craft shop on the way home last night and bought some felt and 2mm (and 3mm just in case) closed cell foam. Probably enough for all of my cameras, for a total of just over $5. We shall see how I do with that. I looked at one of my old Nikkormats last night, and the door hinge seal was completely missing but the area had been cleaned; it seems the previous purchaser had replaced the mirror foam, and had replaced the long door seals with what looks like black wool. So I will start with that camera and give some thought to using wool for the long seals, especially as it has been indicated here that they are not critical.
The Goodman instructions posted above seem to indicate open cell foam for the mirror foam; I haven't found any thin such foam; maybe closed cell or the felt will work there.