Other people have made small runs of custom triggers...but I don't know how the quality is. Bushman put a lot of R&D into his trigger to make sure that it didn't cause any problems with the weapon's firing system.
If you are willing to take the chance, sometimes you can find the aluminum triggers on ebay (they aren't supposed to be on there though, so I wouldn't bid on one myself) and gunbroker. They are fairly rare to come across and are usually expensive compared to Bushman's products. I'm going to wait for Bushman to pick up production again to get triggers for my HP pistols.