Getting the tires off the rims can be a real PITA at times. The steel wires in the tire rust/bond to the rims over the years, which makes it difficult and time consuming to remove. I have used a number of methods depending on how bad the tires are stuck to the rim.
Put the tire in a vice and clamp it close to the rim. Crank down as far as the vice will go. Repeat several times around the perimeter of the tire. Sometimes this will free it up enough that you get the tire to break free. A bit of caution here - It is real easy to warp the rim if you use tire irons when using vice.... just as you have already experienced. Persistence, patience and sometimes some PB Blaster helps. I'm pretty good with "persistence" and PB Blaster but run thin on patience.
Another way is to cut out a section of the tire with your tool of choice. Then use a metal cutting blade in a dremel tool or cut off grinder, and cut the bead of the tire that is stuck to the rim. Just be careful and don't into the rim. Then try to peel off the tire.
The sad part about this is about 50% of the time (personal experience), when I get the tire off I find the rim is so pitted that it is not worth trying to salvage.
I think that NEVH and others have aftermarket rims. I haven't tried a set yet, but cost wise, pretty good deal if you have to pay for sand blasting and paint (or poweder coat).
https://hondanuts.com/08A10A-Rim-Set-for-Honda-Z50R-1980-99-P5787514.aspx
