Fairly big $$$ (about the same as 3 sets of Mahle's) if you're paying for the original forging, after that, the 2nd set of pistons is not too much more than a set of Mahle's, unless for some reason you fell the need for some special metal matrix pistons.
Accralite might have some applicable Porsche pistons / forgings in stock.
www.accralite.com
Cool Fact: Both Omega and Accralite use Hiduminium (RR58 or 2618a) and also blend in other alloys for different reasons. Strong, lightweight, and originally developed for the Rolls Royce Merlin engines.
Stephen
Reinhold Motorsport