Sarah,
As Mike says, the place to go is Tarheel Roller. Having tried composition rollers from other suppliers (which give a great impression, but do not last too long), I tried a rubber roller from Tarheel, and David produced a perfect rubber roller at a reasonable price. I highly recommend Tarheel for your C&P press; I assume you can send him the cores, but if not, he can supply them.
David L. Kent, archivist, Amalgamated Printers’ Association
chirologe@hotmail.com