Hi Tim,
I replaced mine using a set from DIFS:
http://www.sellerie-difs.comIn 2016 they quoted me 205€ for seat+back, including P&P to the UK.
IIRC, remote payment was not easy and so I arranged for somebody to pick the set from Rétromobile as they usually have a booth.
The foams are great and fit very well but they obviously raise the siting position so I now have to move the seat more forward to be able to recline it further (and I am shorter than you!). They are also firmer, as one would expect.
Regards,
JL.