I don't even know if we have a sponsor that sells A/C equipment (Vintage Air is who I would buy from if I wanted an aftermarket product). But I wouldn't expect the vendors to read the boards. I'm just gratefull that they help pay the bills and I have become imune to advertising so any pop's don't bother me as much as having to pay to be a member.
If you want A/C the best bet is to buy another parts car with factory A/C and cut and paste the ducts, lines, and hardware components into your car those parts taht the factory left out of your Impala. If that is too much work, that something like the Vintage Air hang below the dash box can make your car look like it had a dealer installed A/C option (a lot of cars were upgraded that way before they were even sold in my neck of the woods).