The Stealth warships are already here somewhat. The Arleigh Burke class USN Destroyers have had even more modifications to make them have even weaker radar signatures. Dragon's 1/700 USS Mustin kit has many of the features.
The French Lafayette class is availible in resin.
The model making companies are waiting for the new generation of ships appear before the kits are made. The Arsenal ship was modeled and then canceled.
The USN's new DD(X) class will be floating out of the drydock by 2008.
EDIT:
I forgot, Revel issued a kit of the Sea Shadow back in the late 80's when it first appeared. The Sea Shadow (IX-529), was delivered to the Navy March 1, 1985. Went into reserve and was recomissioned on March 31, 2000 for the DD(X) program.
EDIT2:
If you want some more info about stealth ships try http://www.globalsecurity.org