I think Knight is the only one that makes / markets the stuff for a 52 caliber rifle.
Why is your heart so set on this odd ball size?
I would stick to a more common size like the 50, just for the fact you can walk into almost any sporting goods place and get some bullets for it, it will be very hard to find the 52 caliber bullets! and then if Knight thinks the sales are not worth keeping the line you will be stuck with a rifle that you will not be able to shoot any more.