Look in the latest edition of T&F magazine. There is an advertisement for a company (Spears I think) that can get you a complete trigger group. I asked them for one for a new Benelli and was told $300-350 for a new release trigger assembly.
Just talked to them (Spear's) yesterday about a release trigger. You can either send them your trigger and have it converted to release for $135.00, or buy a complete trigger assembly for $285.00.
There phone number is 620-286-5671