| The "proper" magnesiums need some special care when painting to avoid the magnesium oxidising when it's exposed to the air.
The best I've heard of for refurbing mag wheels is Dymag. Not cheap though, about £200 the pair!! I don't think they discriminate against other manufacturers wheels...............
You could try the likes of Dream Machine etc. but it's worth making sure they are going to treat them correctly and use the "special" primers etc. that are required | 
Hybrid Mode
