Finding owner of vacant cabin with no physical address

I would just introduce myself and get to know them and see what their situation is.

I wouldn't throw out a price.  They might think the property isn't worth much and might be worth less than what you are willing to pay. Plant a seed.

Tell them that you have noticed that there's a tree in the road and you would be glad to remove it for them in case they want to visit the cabin.  Tell them you just bought your place and if there is anything they can tell you interesting about the area. 

I assume the taxes are paid.  I always try to find out what their home is like to see what I'm dealing with.  Google their name.  It's not fun to find out when making a phone call that the person you are calling is deceased.  Do your homework.  Know your seller/neighbor.