I used Professional Plastics. And before you say it, the prices on the site are NOT what I pay locally. There aren't anywhere close. I think that's just a generic site. If you search Google for plastics suppliers and manufactures you will get a call list. I spent about half an hour calling the local places until I found the one I use now. They are great and since I've done enough business with them cut the plastic to my spec included in the price of a sheet of XPVC. I can get any color or thickness option I need. I use 1/2" for my racks. I have a 50 x 6qt hatchling rack that uses 1/4". I'm paying ~$85 a sheet cut for 1/2" white. Black is ~$90. The 41qt uses 2 sheets. The 15/32qt tub uses a single sheet. You don't have to be a math whiz to realize the savings in that.
Regards,
B