There are 3/8 - 11mm rings that have a more concave base. Don't quote me, but, I think Tasco bases will work. You'll need to take one of your rings along to compare them. It doesn't take much of a relief to fit a rounded receiver.
Quik Site KS-T90 vertically split rings should work, and as a bonus will self center on any width dovetail. They come in gloss, flat, and silver.5555 TreadwellWayne, MI 48184734-326-1500http://www.kwiksitecorp.com/