There were several companies offering them back in the 70's.......
But the technology has been superceeded since then.
If you're going for a vintage look you'll need vintage mag wheels.
If you want to retrofit newer, lighter wheels that will accept tubless type tires and fit modern tire sizes, you've got your work cut out for you but it can be done.
If you want to go with modern gear, the planning begins with tire selection... choose your desired sizes and choose a specific tire that they're available in.
Then choose wheels that are sized to fit the tires you've chosen.
Then figure out your brakes, axle size and wheel bearing compatibility, find a sprocket to fit the needs of the new wheel and the old bike, and deal with the need to keep your chain line correct. Swaps like this can rival the cost of rebuilding the stock spoked wheels and brakes with good quality parts and new tubes/tires.
It's not that hard and lots of are doing it. to simplify the matter some are swapping the swingarm/brake/wheel as a unit, and the front end form the triple trees foreward, so as not to have to re-engineer too much.
I've got a ton of free info parked at
http://sites.google.com/site/alansdocuments/Do some reading and write down every thought for future reference.
-Alan