Ya, the standard seems to be about -8v off, 15v on. We made a driver on here that does just that. It requires the vla500-01 though, which is out of stock until May.
Ebay might be a good place to find some really big ones nice and cheap:
PRX IGBT CM600HA-24H Power Module 1200Volt 600Amp - eBay (item 350362896821 end time Mar-31-11 12:44:35 PDT)