We do not make any Adapters/Suppressors for break barrels, side-levers or under-lever air rifles. When we have made prototypes for spring piston and gas-ram air rifles we have discovered that the set-screws shear off and the threads strip/break off because of the high amount of recoil these guns produce.
Before things fall apart you realize that most of the noise you hear as the gun fires comes from the piston, which is louder than the impact of the pellet.
I know that isn't the answer you were hoping for, but we won't sell you a product that isn't going to work out in the long run.