As of now, the Rok GP is not a well supported engine. I had to prod Rok just to put a general Rok GP manual on their website, up until then, there had never been any documentation available. If you know what you want you can either have Chi Chi at OVRP order it for you, or call:
Jerry White at Kartworkz or Brandon Jenkins at Allison Racing Engines. Jerry’s website has all the relevant parts diagrams/numbers.
No one stocks parts for these things; they are still way too much of a niche engine for anyone to bother. But the above guys can get you the parts drop shipped from the importer. Rok is pushing pretty hard, so maybe parts availability will improve.