A friend of  mine that works in a brewery in Minneapolis has a used barrel that he is giving away.  Here is what he wrote:
 

I currently have one and soon two Rum barrels that have been used once for barrel-aged beer.  The one already empty had a scottish brown in it, the one that I will be emptying soon has an English Old Ale in it.  They are free to a good home.  Must be picked up here at the brewery.  Let me know if you or someone else might be interested (they also make awesome furniture and rain barrels).

 
Please email me privately and I will get you in touch with him. -Gera crankycat@gmail.com