The main jets are the same as what's used in many carbs so they are readily avaliable. You should be able to get original Keihin or quality aftermarket ones. Below is a link where you can purchase any size you could ever need. Once you see part number you might find another vendor in Iyaly, but these folks do ship anyplace.

https://www.jetsrus.com/a_jets_by_carburetor_type/jets_keihin_99101-393_main_round_28-xxx.htm