Anschutz 5018 and 5022 triggers can be modified to fit using an adapter from Briley, but it's a "sex change" for the trigger. You'll never be able to use it on anything else.
There's the Davies two stage, but they are a bit clunky.
I'm working on a design. It's close and I hope to flood the world with it.
I have one prototype and it's pretty nice.
It won't be cheap though.
Hope this helps.