Make your own.
I use a sma-sma dc-block and a ~0.085 semi-rigid coax with an sma connector on
one end. The other end's ground shield is stripped back an 1/8 inch exposing the
center conductor. This is a "RF Sniffer". DC block I use is good up to 18ghz.
If you plug one of those small 950-ohm Caddock non-inductive resistors
into the end of an SMA female, you get a nice 6 GHz 10:1 passive
probe. Even a carbon comp works pretty well.
And a good fet probe is magical; you can probe a lot of ecl-type
circuits with no ground clip at all. I should think that a homemade
GaAs fet probe wouldn't be hard to make... maybe use one of the neat
NEC dual-gates, NE25x39, with g2 to source for really low Cin.
The best is an SD-14 sampling probe, something like 0.2 pF at the tip.
John