Vector, Black and Decker, Airpro...all same thing with model VEC251B
there are a couple sites online that show it is discontinued or on backorder but this one allowed it to be placed in a shopping cart so it may work for you.
It appears the compressor itself is discontinued.
Part number appears to be 5140044-09
[link=http://www.dewaltservicenet.com/Products/ProductDetails.aspx?pid=69632&tid=15527&AspxAutoDe tectCookieSupport=1]battery link[/link]

if that doesn't work this one shows backorder till 1/3/09
[link=http://www.ereplacementparts.com/black-and-decker-vec251-type-rechargeable-compressor-parts-c-4167_10512_10584.html]backorder link[/link]

try some more with that part number or vec195 may also be helpful. I would also find out if you have one of those outlet type malls in your area there is usually a Black & Decker outlet among them. They may have it or can get it for you. If not maybe a DeWalt parts/service center locally.
Good luck