There are a couple of guys over on TMP (talkglass.com) who seem to have them pretty regularly. You can also use
www.searchtempest.com to search all the Craigslist listings in areas nearby. Sometimes you can snag one fairly cheaply.
You'll also need to obtain an oxygen tank. Again, check Craigslist. I paid $125 total for a 125 and a K. You can use any concentrator that's at least 5lpm, as long as the oxygen purity is 90% or better.