There are 46 different solutions
1. d3 e5 2. Kd2 Qf6 3. Kc3 e4+
I won't try to find all the other solutions!
EDIT: I just realised that is not double check, the word "discover" confused me. Double check seems really hard.
That's not a double check, it's just a discovered check
Ok, I got one for real this time: 1. e4 d5 2. Ke2 a6 3. Kd3 dxe4+. I suppose nearly every legal move works instead of 2. .. a6, so that should be about half of the solutions. Not sure where the other half is hiding.
Swap d5 and the other move. That counts as a different solution
Alright, I guess that's it then! I suppose there are a few more solutions, like 1. d4 e5 2. Kd2 Qe7 3. Ke3 exd4+, and 1. d4 c5 2. Kd2 Qc7 3. Kc3 cxd4+, but apart from that we've probably seen all of them. Fun puzzle, thanks for sharing!
