Do you want the DS Phat or the DS Lite? I know locally the stores still have a bunch of DS Lites. I think they are about 130USD right now.
Old...clunky... I'd assume the original phat ds. Try asking them buddy (as in walk in, they have an extensive stock inventory system and might be able to check other stores), if your in another country, look on the site and have a look...but prehaps you'd be better off on ebay if that's how your intending to buy.
Why would you want the Phat over the Lite though? (I have both, and see no benefit either way, with maybe a few bonuses for the Lite).
-Cost -Tends to be a bit more durable (the hinge on one side of the lite always breaks) -And personally for me, makes a good self defence weapon (helped many times).
<3 my clunky DS :] The DS lite released just before I got my DS, so I just bought the phat one anyway. And also, it's true about the self-defense part. Don't think they sell them anymore though. I'd try eBay if I were you.
At my local GameStop, they sell the DS Phats (original) for $90 USD, used DS Lights $110, New DS Lights $130, new DSi $169.99, not sure about used DSi's.