If you mean the soft foam ,not hard polystyrene, I think camera shops sell it in sheets for you to put in your camera case and cut your own shapes round your lenses and camera bodies. In the days when I looked at camera mags I'm sure there were adverts for it.
When I got my first SLR I became a serious camera nurd deciding what lenses and filters to get: a camera nurd is someone who reads camera mags for the equipment ads and doesn't notice there's a four page spread of glamour pics! (just as Rick F can tell you the guitar behind which the nude model is hiding but not whether she's a blonde or not!)
RtS (no longer a camera nurd though I do "paint with light" occasionally)