You could easily make (or buy -->
Neutrik NYS-SPP-L plus Rean and Behringer 1/4" Patchbays | eBay <--) a patch panel. Just get a bunch of 1/4" stereo audio jacks and wire up them up with the scanner audio on the tip and ring locations (leaving the other as a floating ground). Then make up (or similarly purchase) the patch cords using 1/4" stereo audio plugs wiring the tip to tip, ring to ring, and ground to ground (or to eliminate ground loops if necessary by connecting the ground only on one side). On the jacks, you will connect your scanners on one row and desired output(s) on the other (or however makes sense to you). Patch panels are (or at least were) often used in professional audio settings. Note: If you make your own panel and cords, you can use whatever size stereo jacks and plugs you want. Using 1/8" jacks will allow you to use premade 1/8" stereo patch cables that are available most anywhere (also the panel size will be smaller, which is often a plus!)
Be aware that using the stereo jacks are there to isolate the two audio lines and are designed for mono use. For true stereo use, you'd use a pair of jacks (one for left and the other for right). They are designed for balanced audio. For unbalanced audio, you could use mono jacks but that would force a common ground and could cause issues if your sound source isn't designed to work with common grounds. Also, since most scanners use the external speaker jack it will be unbalanced audio and may expect a speaker or other load to be present at all times. You can fix this using an audio transformer to both provide the load and convert from unbalanced to balanced audio lines. Some radios are designed so their audio must be isolated from ground to prevent damage to the audio circuits. These will need to be wired using balanced circuits! You may still need the transformer to fix the impedance issues though.
A typical 8 ohm (or whatever fits your input/output) to 600 ohm transformer should work fine. Just make sure that the 8 ohm side is on the scanner side and the 600 ohm side is on the jack side. For your outputs, this would still be similar, with the 600 ohm side still on the jack side and the 8 ohm side on your output device side (note, this assumes both your input and outputs are 8 ohms. If your output device isn't 8 ohms you should use different transformers for the outputs.