Forgot the season and which episode it was, but he found them in a "swamp" (actually some forested area up there, not in an actual swamp...), and he pulled the cars out and dragged them both to his shop. Once there, he examined both cars, and decided that
1. Both of them were too far gone (actual body damage, plus the deterioration from being out in the wild for over 30 years, and
2. Neither Charger was particularly rare or even worthy of restoration, as both of them were base models with no notable options on them.

He did remove a few parts for future restorations of other Chargers. The shop had a high school age 'apprentice' and Mark put the kid to work, removing some structural roof pieces that were not damaged and not available in the aftermarket.