I'm not surprised there are only one or two makers of this kind of switching. My perception has been that Array Solutions/WX0B have been innovators in this, as well as their stack switching boxes, an
Top Ten makes good SO2R switches, too. I've been happy with them. Different approach -- separate A/B relays for each antenna and separate 1-of-6 relays for each radio. This might provide better isola
I would recommend a look at <http://www.qth.com/topten/apnote1.htm> which explains how this works. Their A/B selectors have one excellent feature which is unique so far as I know, a hardware lockout