Its not really a drama or hard to do, its the norm when your talking bikes from 1980's and older, they are not the current range of Mxers so no companies are not mass producing rims to suit old bikes with drum hubs, everything is custom drilled or modified to suit the applicatio. Many wheel places specilaize in doing that. You might be able to buy new genuine rims from Yamaha if that sounds easier to you, but really all you need to do is phone or email a rim supplier such as the 3 above and tell them what bike you want it for what colour rims and then they will drill them do them for you they should have all the data on your wheels, if not they will ask you to measure a few things or take photos to send them. How hard is that? The hardest part for you is to hand over the $ for the new rims
Yes the old rims are known to crack after a hard life, its nothing out of the ordinary.
