I was at a landscape store earlier this week and asked if they had any pots they didn't use.  He directed me to a shed and said 'grab all you want'.  So I gathered the largest pots I could find, including one 45 gallon pot (30" x 20"). 
Seeing I won't be using the huge pots for several years, how long can they withstand sitting outside year after year?  I didn't want to pass up the opportunity to get these large pots.
The 45 gal is not as strong as the pots you see on the left.  Those seem like they'd last a long time.

Good find, They will hold up along time, very Sun/UV tolerant  I have some I have probably had 20+ years Nursery grade pots  are better than the ornamental pots you buy and 10 times better then the totes folks use

Good find Frank, to protect from the sun's harmful rays, you could always get yourself a nice cheap black tarp and cover the entire gathering of pots. Uncover when you need one!

Good find and always smart to ask!!! I have found some very cheap ones on Craig's List.

That's an amazing find Frank, you should go back and get more, try to have planned potting gradual size change stock. 1gal, 3 gal, 5 gal, 10gal, 20-25 gal and so on...
My fav nursery sells the used ones for $3 for each 15 gal ones, is it a good price? The new ones go for $10 same size.

Unlike regular plastic bins, black nursery pots last many, many years. I try to store my empties in the shade.

Good find, congrats. It's more difficult to find those larger pots. I've gotten quite a few of the 15 gallon size over the years. Sometimes at yard sales you can find a few, and as someone said, Craig's list. But you have to watch regularly. I think I finally have enough.

Thats why i always say- You find a pot and you got one more fig tree for free.

The ones on the right pic are them thin (flimsy) pots and may not last that long.

Some on the left pic & thick-plastic with a solid-top-rim are my favorite...

Hi Figgyfrank,
Good find.
All you need, is to protect them from the sun, the rain and the frost.
If I were you, for the pots inside another pot, I would check that some are not locked one to the other, and unblock them if so .
With time, they are harder to separate and do break when you insist .
So now all you need, is compost and new trees ...
In which USDA zone are you ?

My recommendation: put them in the shade.  Heat and sun will degrade them faster than anything else.  Also, if the flimsy ones start to get small cracks or tears, you can duct tape them to prevent them from getting larger, and maybe get a little more life out of them.

Thanks so much for the advice, everyone!