The Claws are not too-expensive; not too-cheap freewheels from ACS.   They will thread onto any hub threaded for a freewheel, as well as hubs threaded for a track cog since the thread pitch for (English threaded) track cogs and freewheels (multiple and singlespeed) is the same.

If you need something larger than 18T please call the shop.  We don’t at present regularly keep the larger tooth counts around, but we can order them as needed and ship them out in 1-2 days.