I have found the best way to score major wood piles is to find a good logging crew working, a deed far easier than you would expect.
I hang out at our local sawmill anytime I am running low on wood. Watch for the trucks coming in and talk to the drivers. I even shoveled sawdust under the mill just for the excuse to hang out. But on the plus side, I have never gone home empty handed.
I talk to the drivers, and if they got something for me, I follow them back to the site where they are logging. The driver has already supplied me with the name of the crew's boss man, so its a simple matter of walking up and asking permission.
Last summer the boss man was plumb glad to see me, he had a stack of culls that he wanted gone, they were in the way. i would drive up with my 16ft trailer and stand in line with the logging trucks. When my turn came up to pull up under the knuckleboom, he swung the loader around and pulled from the cull stack and loaded me right up.Never broke a sweat.
If they arent any culls around, you will always find cut offs by the loader, and many times they will load you up to get you out of there and out of their way.
As far as cutting tops, I have found that many are willing to let you cut, but they want you to do your cutting after they are finished for the day or on the weekends when they arent working.
A case of cold ones go a long way in persuading them to let you load up.
Just my two cents worth.