Why is it nobody ever asks a question like this until I clear out my magazine pile and toss the old Butane Propane News and LP Gas magazines?

No promises, here are a couple I peeled from old BPN classified's. They may be out of date. BPN doesn't put the newest issue online:

USED PROPANE AND AMMONIA STORAGE TANKS FOR SALE LOCATED IN VARIOUS LOCATIONS UP TO 60,000 GALLONS CALL: 267-784-4251 EMAIL:[email protected]

6,000-30,000 LPG Used Storage Tanks, guaranteed to meet codes, nationwide availability, will buy or trade for your used storage facility. PH-239-287-3726

You might do a Google search with the phrase: propane storage tanks for sale I got several promising hits from that including

http://www.totalenergy.com/

http://www.lpgventures.com/

http://www.storagetankspropane.com/

http://www.transtechenergy.com/ocala-30s/propane-storage-tanks/used-propane-storage-tanks/

Another possibility is downloading LPG mag's Supplier's Guide. Be warned, it is a big pdf file to downloadhttp://www.lpgasmagazine.com/lpgas/data/articlestandard//lpgas/452009/638552/article.pdf

EDIT:WOW!  Don't know what happened to the formatting.  That is NOT how it looked when I hit the go button.  Let's see if I can clean that up and make it more readable.