Just a thought...have you explored the entire land mass? Are you so certain that the only junk piles are the ones right by the starting towns? I have spent the past couple weeks running all over the damn place. I found tons of junk piles in the most unlikely locations like on the top of mountains, etc.
Is finding these secluded junk piles easy? Not as easy as plopping down right where you first spawn in game, but not really that hard either. For the solo'er who doesn't want to deal with the crowds, a little exploration will probably go an awful long way.
Remember, a large tribe isn't going to bother with a small junk pile that is not near a large flat area. Not many people want to terraform an entire freaking mountain.