GN250 needs a new carburetor

I'm trying to fix up my brothers GN250 and i want to fix up the carburetor but i cant find any repair/rebuild kits for it. Would it be possible to replace it with a different carburetor? it currently has a MIKUNI BS34SS and i cant find parts for it that aren't stupidly expensive. Does anyone have any suggestions on what carburetor i could replace it with?Thanks in advance, I'm new to working with motorcycles via /r/CafeRacers https://www.reddit.com/r/CafeRacers/comments/gda6jz/gn250_needs_a_new_carburetor/?utm_source=ifttt