Filigrees
Costume Jewelry Supplies (excellent site overall!)
Fire Mountain Gems (semiprecious stones, glass beads, metal beads, miscellaneous natural beads)
However, I get a lot of my supplies just from the regular craft and fabric shops like Michael's Crafts and Jo-Ann Fabrics. And the eeeevil Wal-Mart. And some interesting vintagey stuff from yardsales and junk shops.
Softie...you can make fabric flowers by ruffling a piece of ribbon along one edge, then coiling it up along that ruffled edge, stitching it to lie flat. That makes a rosette. Otherwise, you can cut petal pieces of any shape you like (triangular, oval, and heart-shapes seem to work best) and stitch them together in a little bouquet.
This one I made as trim on a hat I made for a client. It is meant to look quite a lot like a Poinsettia. These are the triangular petal shapes. I made a little pleat in the bottom of each petal to make them look fluffier.
This one I cut a long strip of fabric, then cut large scallops in one side of it, zig-zagged the raw edges, then gathered the straight edge and coiled it, as one would do to make a rosette. The green leaves are large triangles with pleats in them.
Both of these flowers are very large, but one could make similar ones which were smaller. The red one is about the size of a coaster for your coffee mug, and the pink one is bigger than my hand!