I bought a approx 2.5 gal new oak barrel from a website. It's got a char on the inside. I then bought my own whiskey/bourbon to put in the barrel to "age" the barrel. I left it in there for 4-5 months. Drained it and filled with syrup. Aged it for 3 months and just bottled. It's amazing. I then backfilled the barrel with the bourbon to potentially impart some maple flavor into it. Now, you can't sell this bourbon but I can gift it to buddies of mine. It's hard to find freshly drained small barrels from distilleries. The smallest you may find is 5 gal. Next time I may have buddies of mine go in on the bourbon with me, as it's not very cost effective to go this route on your own. I think I paid just under $100 for the barrel. They sell these barrels up to 5 gal size.
https://www.barrelsonline.com/
This was the website I got my barrel from