Hi Kevin,
With the Yaesu VX-8R, you can do a mod to wideband that fucker and get on the drive-thru frequencies, as long as you know what frequencies they are using and if they are using PL tones. I've noticed a lot of drive thru places use standard carrier access and radios/headets are on different channels, so if you do the wideband modification, you will be able to transmit at 5 watts (more than enough), all the way up to 470 mHz.
Other ways of finding drive thru/retail store frequencies:
If you have a general idea of what frequency range your target is operating in, you can just do a search on your police scanner and it will eventually lock on to any nearby transmissions. This is tedious but it does work. Another similar, but less aggravating way is using the close call function on your scanner (if it has one) to locate any nearby signals.
The third option is the best but the most expensive, and that is to go out and buy a handheld frequency counter. Gigaparts has a handheld MFJ one for 120$. All you do is go near an employee talking on a headset or radio and when they key up, your frequency counter will display what frequency they are using. These are VERY handy.
I think the VX-8DR requires removing a diode or a jumper, and that is easy shit. I did this to my THF6A years ago and with your Tone decode function, you can also find out what PL tones stores are using
Good Luck!
Just type in Yaesu VX-8DR Mods and it will come up.
Best Regards,
Mister Skin