There is a store locally to me called TAP Plastics... they carry all sorts of stuff polycarbonate. I would check your Yellow Pages (do they still have these, or am I too old?) for something local to you.
If your looking for a sight tube, buy some from BobbyM at Suebob.com. I bought two polycarbonate sight gauges from him at 15 bucks apiece. I'm pretty happy, no melt downs and no worries about glass breaking. I modified them for my kegs and it turned out awesome. Take a look at how it turned out. I basically covered his tubes with 1/2 copper, put a cap on it, then covered the screw with copper that I tapped into the keg. Oh, also, I used a grinder to grind the groove to see the pipe. Suebob.com is the way to go and cheap cheap.
snake10
You'll have to excuse me, I'm a little new to the home brew discussions.
I know you said that you wanted something local but I found an online store for some very inexpensive tubing to make some pretty sweet sight tubes with the following materials. Some of the materials were from Home Depot.
Home Depot
3/4" washers (2)
6" x 3/8" bolts (3)
3/8" lock nuts (3)
1" (ID) to 1/2" copper sweat adapter
I guess I should clarify that the sight glass that I constructed was an INLINE glass and NOT for showing tank levels. However it is really cool to show how the wort is clarified as I recirculate it the runoff through the grain bed.
I think polycarbonate tubing is kind of an industrial specialty type thing. If you have an Grainger, Mcmaster Carr, or MSCdirect locations nearby, you might get lucky. As mentioned, plastics manufacturers with factory storefronts might work also.