New ignition switch
MiMitch,
The new key must have the same resistance chip as the old key, in addition to the grind matching the new tumblers. So, you likely need a blank key having the same resistance as the old key. Then have it ground to match the new tumblers.
The alternative is to bypass the VATS as Tobben described above. But that's a nice feature to keep active.
Good luck.
PS The dealer may be your only source for a blank and may be able to determine the # (resistance) of the old key. In my area, there's a very well equipped hardware store that carries a full array of GM key blanks - even a full set of VATS blanks. Check around.