I think leasehunter.com is probably the best of the pay sites. Actually you don't have to pay to just view their lease listings, but you do have to pay to view the contact info for a lease if you're interested in it. Craigslist also will have some leases on it. And of course, folks will list leases on this forum.
However you search, you've got to check for new listings often and be able to act quickly to go visit the property and pay the deposit because the good leases get filled pretty fast. Good luck.
Walk the night, travel light, cross the Rio Grande
Someone strums a mandolin, soft gulf breezes blow
My new life is waiting in old Mexico
-Robert Earl Keen