After market triggers!
There are the trigger parts approach, both adjustable and just drop in. There is the Timney drop in trigger module approach. There are single stage and double stage triggers available. For a lot more details go to the Brownells website. They sell al kinds of gunsmithing parts and the AR platform parts is one of their biggest selling areas.
I bought the JARD adjustable trigger and installed it. Adjustment is critical. Get it too tight and the gun may double (don't ask how I know that, and yes the gun was illegal at that point). Adjust it too loose and there is a lot of creep. If I had to do it again I might select a different manufacturer and a two stage trigger. After owning a couple of European guns with two stage triggers I have come to think they are a better way.