And when it does exist, it quite dodgy in most cases.

Go on ebay and buy either 1390 or 1490 Dell (truemobile) PCIE wireless card.

Cost between 5€ and 25€

For example;

http://cgi.ebay.es/NEW-Dell-Wireless...3%3A1|294%3A50

The difference, if my memory serves me well, is 1490 has a/b/g while 1390 only has b/g...

But anyways, both of these are native Airport devices. 2 minutes to swap them out. dead easy