Mcmaster Carr for sure. Especially if the project is funded and time sensitive.
We also have a pretty well organized recycled bits and parts library. This was only possible once we brought someone on who had the temperament and desire to maintain it. Its a pleasure for him to search and modify, and he hates buying new when he can make do. He will save and index a 4" x 3" scrap of plywood. And he will remember that he has it four months later.
If you are ever in the Providence Rhode Island area, RISD has two amazing art supply stores, one focused on 2D (Paints, papers, drawing tools, etc) and another on 3D (All sorts of amazing sculpting materials and tools). Both are well worth a visit if you're in the area!