I'm purchasing a GR2 and finding that the counterweights that fit the 20mm shaft are primarily Vixen, available only through Orion. I'm looking for about 15 lbs. The Vixen combo for 15 lbs is more expensive than the Astro-Physics or the Carmel Coast Stainless Steel CWs, but these fit the larger shafts for AP and Losmandy Mounts. Also, the Vixen CWs are smaller diameter, taking up too much shaft for heavier scopes, therefore less torque adjustment.
If you have used CWs that have a 20mm ID I'd be very interested. Otherwise, I believe supplying quality SS CWs with a 20mm ID would be an excellent start up business, because of the apparent lack of supply, especially with the GR2 entering the US market.