I've finally managed to find somebody to redo the seats and foams, price not yet final as of now.
Good thing is the company is located in the US so there will be a lot less to-and-fro.
The base will be fiber but, once covered, will look stock. Nice and fine. The bottom is gel-coated black. Looks stock
(how many times do you look at the bottom of T500 seat?
)It's Brad from HVC, you can check the previous repros he's done here: http://www.hvccycle.com/seats.html" onclick="window.open(this.href);return false;
As we are giving him a sample, we get the first batch at a introductory price.
After that, it will go back to normal prices for the general public.
I think Muzza, cyclebuster and me need one complete (pan + foam) set. I might need a 2nd one.
That's 4 of us, the more we are, the more likely it's going to happen as it helps Brad recoup his tooling cost.
Covers are readily available at very different prices… your call.
Jim, are you still willing to send your pan and foam?
For myself, the edges are completely rotten away on mine, but the upper surface is intact - I will either fab up the sides, or perhaps pick up another pan with good edges off something else and splice in the edge I need to secure the cover to. That would preserve the stamped pattern and shape and so should work OK. 
