Hi,
Grizzly Tools has some curved plastic humbucker rings that are very inexpensive. If they don't work, at least you wan't be out much money. Because they are plastic, you also might be able to modify them somewhat. They also have a very thin metal ring that you could probably curve to shape.
Peace and good luck,
Dave :
Yes Grizzly fits and I thought I would post this if anyone was in the same boat and needed rings for a chinese clone. I am impressed with the two things I bought a nice LP switch and the ring. Nice quality for the money.