Here in Phoenix, there is a place called Laird Plastics I used to go down to and buy mostly from the scrap bin. Nice people, at least several years ago last time I was there. Whenever I asked about something I didn't see in the bin, if they didn't have it at all they'd offer to order some for me (I never did that, though, as I couldn't use a whole sheet or roll at a time). When I was building this:
and this (the one on the left):
and some other little props to go with it, one person was interested enough to give me some little "keyrings" of old samples of various fluorescent plexiglas colors, to use for data crystals and whatnot.
I don't have pics of those, though.
THey have two locations in PA, too:http://pittsburgh.lairdplastics.com/ind ... =67&MCU=52http://philadelphia.lairdplastics.com/i ... d=67&MCU=5
If you don't mind ordering online, there's a number of places.
This place:http://www.professionalplastics.com/ABS ... RMINGGRADE
is where a guy that consulted me on vacuforming some small project boxes got his. (don't know how it worked out, though; never heard back from him). What he showed me looked pretty good; flexible, didn't smell funny or craze when heated with a hair dryer up close, etc.
They also have a clearance section:http://www.professionalplastics.com/Pla ... sInventory
They show up at the top of a google search, too:http://www.google.com/search?q=ABS+sheeting
which is probably why he bought from there, if they also did a year or two ago.
The google shopping search turns up some stuff, too:http://www.google.com/products?q=ABS+sheeting