Hey There
I used to work for a hardwood company which sold exotic and domestic lumber
The "stickers" which are chunks of timber banded on the bottom of the units of lumber often are made out of the same wood they sell as lumber.
Many a times I took these home, lots of red/white oak, ash as well. A lot of this wood was chunky 4"x4" and up to 42" long.
This was "junk wood" which typically was used to band together another stack of lumber, or simply thrown in the scrap bin.
It might save you some time with sawing and cleaning up RR ties if you have a hardwood company in your area.
More times than not, these guys will give these stickers away. It would be wise to tell them it's for firewood though.