It's kind of expensive (because SMA connectors aren't free), but one could probably make a little protection board with a SMA jack one end and SMA plug on the other, with the TVS diode on the single microstripline trace in between.? Sort of a dual "connector saver" and "VNA saver".? The parasitics of the board would "calibrate out" for the most part.? If you had a steady hand, you might be able to build one out of just the two connectors, if you get the kind with the posts - solder the posts together and somehow put the diode in between. I've done this for making a T or for oddball loads, but it's not something you'd be proud of.
Soldering the diodes directly on the pcb is easy and you can never forget them...
See pictures (follow the trace from connector to series capacitor to TVS diode to resistive pad (3 resistors). The other port has the TVS diode directly at the input (protects the capacitor too)
