Games Workshop has massive amounts of supplies (pricey, most are quality) and articles (most using their products, but similar to many other companies):
Though I don't play many of their games anymore, I gotta give them props for the terrain!! Poke around the site, there's DAYS of material.
Basic supplies (in big 'box' stores):
Hardware stores have things like pink foamcore and Liquidnails, not to mention large amounts of mark down paint. Most can also 'color match' any sample of paint you want replicated.
I'm sure there's more, but here is a start.