Most Euro kart frames will accept a lot of part from Rigetti Ridolfi (sp), SKM and Wildcart. Basically, there are a lot more trade names out there than actual kart manufacturers, and many of the parts are defacto standardized, or have common bolt spacing that allow one “brand” to be substituted for another. So, items like master cylinders, brake rotors, hubs, steering columns and so on are pretty easy to find even if the frame manufacturer (like Hasse) isn’t selling them under its nameplate.
HOWEVER, there are enough differences that if you don’t know what was on the kart originally, you will have a very difficult time figuring out which particular aftermarket part actually fits your exact kart. You’ll continually be presented with 2-4 options and no good idea as to which is correct until you actually grab the parts and see what fits. I don’t envy you and I think you’re looking at a lot of frustration.
Finally, these are full competition karts that are not remotely suitable for “bashing around in your back yard,” unless you are particularly fond of broken ribs, injured spines and that sort of thing. At least, I hope you are not planning on putting anything over about 6hp on this thing if you ever get it running.