I bought my Jensen Neo 15-150 from Antique Electronics Supply; they stock them, along with a lot of other good stuff:
http://www.tubesandmore.com/
I've had the Neo in my Delta Blues for about a month now, and I really like it so far. It's warmer than the stock speaker, but also more articulate, and it takes my pedals well. I haven't gigged with it yet, but I've been really cranking it breaking it in, and it sounds great.