I want to be able to move my stock between 2 rifles, so I only need the tube.  Anyone know of a vendor selling this as a stand alone item or am I stuck just buying another one?

I would go directly to Magpul if you want just the tube. Not to be a jerk but why not just buy another stock?. I'll bet just the buffer tube won't cost significantly less than a complete stock.

Might be right, but I'd at least like to find out.   If it's half the price that's at least $100 saved.
I"ll call Magpul and see.

Actually, something just came to mind. I'm looking to replace the black tailpiece on one of my Magpuls with an olive drab one. I know Richard @ Magpul "pretty" well (never met him in person but I've talked to him on the phone quite a few times) or at least well enough that he knows who I am. I'd bet we could work something out with him where he could split the cost of the stock between us then just ship you the buffer tube and the tailpiece to me. Heck, I'd have an excellent condition black tailpiece I could sell you are a great price (seriously, it would just be an extra that I could have not use for). I am completely serious about this. Richard offers excellent customer service and I'd bet he could help both of us out. Send me an IM if you're interested and I can try calling him tomorrow. I'm almost 100% sure he would help us out.