I would be selling the rims and buying some second hand to suit. I haven't seen any adaptor plates but I'm sure something exists but whether it is worthy..I'm not sure..
As for changing hubs over you'd have to check the wheel bearing O.D. and try and match it with something that's 4 stud.. i doubt you will get something to match..unless someone here can help you. Just easier to get the wheel to match what you got