CZ6a coil question

I have a CZ6a with the stock coil. Is there a larger coil out there that would work on this machine and be suitable for coinshooting? I'm hunting a park where the old silver is now coming from 10 inches down and deeper, and I'm having a tough time trying to pick up a decent signal from it with my stock coil.

It's a Dankowski-modded CZ. When he worked on the machine, Mr. D. wasn't happy with the depth he was getting in his bench tests, either.

the 10.5 coil by fisher

you have 3 choices from them

the 5 in
the 8 in
the 10.5 in