I want to try my hand at a local field and target competition and I'm told I should get a scope wheel for the parallax side focus knob on my Athlon Argos BTR GEN 2 6-24×50 FFP mil. It appears the knob is about 32 mm in diameter and has grooves in it. Any suggestions on what I should be looking for and where I can get one would be appreciated. And if someone has one to sell let me know.