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.
He's got an M4-0050 that goes 0.5-50 GHz, too.
- Kirt B.