Academy should have them, though the price will be high. I used to get them from a barrel manufacturer in Houston. It's possible, though not too likely, that there's a barrel marketer in DFW. The people in Houston made them at their plant, so they'd sell me drums that didn't make spec, so they'd be cheap ($10). Also, google up OnTime Feeders and they'll ship to you. What I don't know is where their price is versus Academy. My 30 gallon barrels have held up over the years, but the tops will rust out, so I get them from OnTime.
I assume that you'll want the type drum that has the open top, rather than having to cut out the top yourself.