Marki Microwave has always had one
of the widest selections of mixers that I have seen. They
happen to have one to meet your requirements. I don't
recall the owner's name, but he gave me a lot of help a
few years ago with a particularly tough requirement I had
for an airborne defense project. The guy did some actual
testing for determining spur levels for me prior to ever
even buying anything from him.
Look here for
He's got an M4-0050 that goes 0.5-50 GHz, too.
- Kirt B.