The best way to find lease land is to drive around and find vacant property, go to the courthouse and find out who ownes it and then contact them and ask if you can lease it.
I looked for a lease pasture for a long time. Most of the stuff around me had been spoken for for many years. Some leases even handed down.
The only other option, and I wouldnt do this, but I know someone who did, was offer more money when they new a lease was up for renewal. Personally I sort of think thats just a bit underhanded when dealing with neighbors, but from a business standpoint I dont see anything really wrong with it.