Any particular type in mind? There's some high-end stuff and I think some low-end stuff - cassette multitracks - still available new, but nothing in between.
I believe Otari are still selling the 2-track MX5050, but they are going to be very expensive new.
I'm not sure if Studer still have any of their A827s left - in any case they cost about the same as my mortgage deposit :-/
Oh, and I think ATR Service can probably sell you a rebuilt Ampex ATR 102, but I hate to think how much it would cost.
In all seriousness, your best bet would be to look on ebay or similar. For a good starting multitrack, consider the Tascam 388 or maybe the Fostex R8 (this one will require a mixer as well, though). But you will have to take care to avoid being stung, unfortunately.
For a mixdown deck, there are a lot of options. The Tascam 22 or 32 seems to be a favourite around here.
At the end of the day it decides what you're planning to do. Some people get a multitrack and track the song on tape, then import it into computer and finish the song there. Some people track the song on computer and then mix it down to tape. And then you have people who try to do the entire thing on tape and only digitize it at the last stage so.