The only ones I've seen are in the Esslinger catalog. My old '97 catalog shows cranks that will get you up to 2850cc's with a stock block.
They aint cheap, however. The '97 price list shows the kit (crank, pistons, pins and rings) at $1400.
On edit...
Esslinger's website appears to be down at the moment, but I just found a recent (12/03) flyer from them. It shows a 3.875" stroker crank (2850cc) goes for $1475. Apparently this is the price for the crankshaft alone.