There are some 6 inch / 3 hole go cart rims that are available out there. I suspect that one of those would work. Something like this:
https://www.jackssmallengines.com/ja...yabegi0bfd_bwe
or this:
https://www.bmikarts.com/6-X-4-Rim-3...SABEgJkOvD_BwE
You may have to double check the specific measurements but this would at least get you a start.