When in doubt, try colleges. Most of them have so much money toward band funds, that they basically give them away. Ask around, call the directors, and maybe even check your local music store sometimes.
I had an old director who bought an Adams 5 oct. marimba for 3k. Good luck!
Well, marimbas and other larger xylophones are really expensive and hard to find. My school has 2 marimbas and a vibraphone. And from the looks of it, they're very expensive. I guess I could ask in a week about how much they cost, and where they bought 'em.
But for now, try a local music store, such as Melhart's. They have these awesome percussion kits containing a practice pad and a small xylophone. (With a stand to hold it of course.)
And, a word of advice, don't hold that stand up horizontally; it go break-break DX.