www.historicaerials.com has a ton of old imagery for free, but its coverage of El Paso is no good.
When you go to Google Earth (if you have that program installed) you can click "Historical Imagery" under the "View" menu, and then you can see your options for images going back into the early 90s. They have coverage of El Paso that goes back that far.
I've bought images from USGS before and they do not have the high resolution images your boss is talking about.