Do you really need the clear acrylic in the form of toothbrush handles?
Seriously, though- the web has made ordering stuff like plastic stock quite easy today. Google helps you find it, and more and more big retailers are now catering to home hobbyists and handymen by dropping ordering minimums and such. I have gotten good service from a place called US Plastics, but there are a number of other places. And, fed ex and UPS have really gotten time reduced on delivery- I frequently get stuff ordered on internet in two or three days. Most common shapes are sheets and round rods, but some places do have other shapes.
I now keep several diameters of rod stock on hand and a sheet or two.