Sorry for the delay... too busy to reply! I was doing some research as Big Rich told me. And yes, they are compatibility with other Suzuki models. I guess the most important think to consider are the hubs. FYI: I´m in Argentina, zero parts to find, only from 1979 to 1982 they import motorcycles and closed again for about 10 years, nowadays with the goverment policies is a pain in the a** to import new or used parts, however everything is possible. So, if i bought something in the US I cannot make a mistake with the part number.
I found http://www.cmsnl.com/suzuki-gs425-e-1979-usa_model16012/partslist/ (as many others) intresting because you can find a part and compare with another motorcyle or do a global search with the part number. Attached are two text files with hub models (front & rear) and the ones that they used the same. As far as I can imagine, having the correct hub, it´s easy to find a rim and spokes to complete the wheel and using the disk, drum and all that stuff of the mag wheel.
A month ago I found this offer. I contact the seller but he has no idea if they were compatible. After all the research I did, I guess they are OK.
78 Suzuki GS400 wheel front
http://www.drumhillcycle.com/Used%20Suzuki%20Parts/fuseaction/viewProductDetails/productId/3,3879063
78 Suzuki GS400 wheel rear
http://www.drumhillcycle.com/Used%20Suzuki%20Parts/fuseaction/viewProductDetails/productId/3,3879062
Keep me posted if you go forward with this... Sorry for my english...