Remote aux I/O from one radio to another is done by fleetsync and is a special type of status message. There are a total of three available.
The radio has nine programable I/O ports available on the rear 25 pin connector. Any of those nine can be programmed as an input or an output. Input is easy. All you need is a dry contact closure to ground to make it active. A simple switch is all you need. The outputs are tricky. They have almost no drive at all and are pulled up to 5 volts. A buffered relay is what you want to use on these and this is what I use with good success:
ELK-924 Sensitive Relay
Now if you need only one or two outputs, code3cowboy mentioned pins 15 & 16. These can be used and are output only. Nice thing is they are open collector and can sink 500 mA of current, enough to run a small relay directly ( coil 100 ohm or more is perfect).
To make this all work, first the pins used from the DB-25 need to be programmed under "extended function". Then basic fleetsync parameters (fleet, id) need to be set up as well as the target radios id (this is to which "output" radio changes state when the "input" radio changes also).
If this is the first time someone has done this, they will need to have both radios with the input switches and output relay attached and the the programming computer handy 'cuz I will almost guarantee it will not fly right on the first go-around and some trial and error testing will be needed.
If your radio shop doesn't have the guts to tackle something more than just putting freqs and PL's into a radio, I would find a shop with people that are a little more knowledgeable.
If you want to read up on how this is done, here's a link to a PDF manual (about 3 megs):
http://dl.dropbox.com/u/2991846/TK-2180_7180_FUNC_v200.pdf
Can you program your own radios or are you stuck with your dealer to do this?