for casters, try "American Science and Surplus" - http://www.sciplus.com/
just search for casters, you'll find some random ones cheap.
This is a fun site to browse, lots of junk, not much science, but I've picked
up a number of junky things like dental picks, hemastats, tweezers, etc. that
you don't mind bending or breaking since you didn't pay much for them....
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