Believe it or not, the home Depot near my house had a gallon can of the resin, complete with two tubes of catalyst. I believe it was Bondo branded, even cures in two hours! Works great for me so far.
They even the fiberglass mat, but only in small sizes.
If you live near the water, check out a boat supply store. I live near Annapolis MD, and the boat store I went to had everything, it was like a candy store of Fiberglass materials.