I use Arca-Swiss style plates on all my photography gear. I just added a plate to my spotter and use one of my camera tripods for the spotter. I also have a window mount I made out of an old camera ballhead that also uses the plates. You'll need to get a system most likely where all of the heads you own for your tripod and window mounts will use the same plates. I really prefer the dovetail style plates over the octagonal shaped ones. The dovetail plates can slide in quickly and you can leave a screw in as a catch/stop so the camera/scope can't slide all the way out.
I got mine from Wimberly but any of the major photo stores can set you up. If Cameraland is a sponsor I'd try there first.
Wimberley Professional Photo Gear - Camera Body Plate::