Last real new N900s were at Newegg but quickly sold out months ago AFAIK.
Buying used is always a crapshoot with the USB port issue but I got one in really good shape about a 16 months ago.
I would always avoid the so caled "new" Hong Kong/China N900s. Search the forums; it seems that they take a broken N900 put the functional guts inside a fresh new plastic case, do some nasty repairs and sling it out on eBay for about $200. Every one I know of has had the old apps and user data on it, my Hong Kong N900 couldn't reinstall corrupted apps as the / was partly corrupted, it bricked when I flashed it, won't go into flash mode anymore.