TAP Plastics will make a 1.5" thick platter that is 12" in diamter. I asked for the price to make two of them which, when attached together, will make a 3" thick platter like the Teres platter so that the Teres bearing can be used. The cost for both platters including polishing is about 275. You would then have to get the platters drilled for the bearing. Ideally, a machine shop would counter sink the top of the platter for the record label indentation. I am going to find out about that aspect prior to proceeding with ordering the platters.
If you do not want to "attach" two 1.5" thick platters then the 2" thick piece is the best TAP can do. Attaching the two platters together might make it easier to fill it with lead/sand/mercury..whatever. Probably some good bolts from the underside would do the trick just fine unless anybody has a better idea. Perhaps dowels from the top platter inserted into holes on the bottom platter and glued together.
An acrylic base can be made the same way by TAP; ie, use two or three pieces sandwiched together to come up with a thick, inert, and heavy plinth and armboard.