Is there any way to recover a deleted Lander or buy a new one? I believe that's the reason I have run out of regolith and am not generating new Reg.
No way to get it back once you have deleted it.
You may just have so many regolith compactors running that the miners can't keep up. I usually run into that problem early on in a new colony. Just deactivate all your compactors (you can click stats on just one of the compactors and click "deactivate all"), build a few regolith mines with something right next to it that can accept reg., and mine them. Once you build up some reg, you can build a long strip of mines and like 40 or so miners and mine very quickly to keep up with your compactors. Once you've got your operation going strong, reactivate your compactors and you'll be good to go. You'll have to keep building mines periodically to keep up with demand.
EDIT: Oh, and if your map is completely our of reg, then once you deactivate all your compactors and all the buildings that consume reg, such as steel factories or whatever they're called, you'll have to recycle a few buildings for more reg until you can afford a mine. Mine that, use that reg to build more mines, and slowly build up your supply.