If you can't find a good option for a long distance unsupported ride, then the classic answer is loops. Pick a 50 mile from your house and do it four times over = double century. But unlike going 100 miles out and back, you're never more than 20 or 25 miles from home, possibly much less depending on route planning, and you can do your resupply there every time you come round.

However I think the willpower is harder when you're doing loops like that. Certainly a key factor in completing my first 300k instead of DNFing at 200k was that I had no practical way back to the start and my stuff except for riding the rest.