Do you require them to transmit or only receive? As for transmit capability, I was looking at duplexers and triplexers and could not find any in my search that allowed two radios of the same freq range to transmit via one antenna. That doesn't mean there isn't one out there somewhere, only that I didn't find it during a quick search. Diamond and Comet both market these items (as do others I'm sure).
Now if you want receive only, then you could use a signal splitter. Looks like the letter "T", with one input from antenna and two outputs. No switching, but be aware that you will have signal loss with that scenario as it will split the signal received between each radio. Another option would be an active multicoupler, that provides enough signal boost to overcome the loss of splitting the incoming signal. Stridsberg makes multi-couplers.
Not sure if I answered your question satisfactorily, but hopefully the above is of some use.
Scanners: BCD996p2 || PSR-600 || Pro-668 || Pro-651 // Shortwave: Drake R8A || Drake SW-4A || Tecsun PL-660 // FM: Onkyo T-4310R || Onkyo T-450RDS