I guess you could consider the Astron 'too strong' in one sense: According to the spec sheet the surplus amp mentioned above works on 13V MAX, 12V nominal, and if your Astron puts out 13.8 - 14V as it should, you probably don't want to put that in to the amp. I don't have an amp like that at this time, but I've learned the hard way not to be casual about a max voltage spec.
The surplus amp draws a little over 1/2 amp, and there are numerous small power supplies available that handle that kind of current. You want a regulated, linear supply. Switchers make noise, and unregulated, well, personally I like knowing that the supply voltages to my stuff doesn't move around too much.
You would have to solder wires between the supply and the amp, most likely - and if that's really an obstacle and there isn't anyone you know locally that might do that for you, then it goes back to a store-bought solution, probably. The Stridsberg multicoupler wants 12V, too, but only 85 mA - and you'd still have to have the right power connector - so it's just slightly less complicated.
Or you could accept about 6.5 dB loss, which unless you're trying to get weathersat imagery or radiosondes, or non-repeated comms from two counties away, something like that might not be a show stopper. You'd just get a nice passive splitter similar to what's in prcguy's pic. Of course there may be someone who will tear my head off for mentioning such a thing.
