[Baron Von Zeppelin]

There is debate about the Buick list that lists some multi-make dealers.
I tend to go with it usually on those.
But its an open ended deal sometimes and hit/miss.

You can contact Mike Noun (PY Member) who has deeper resources than anyone else on dealer codes. He makes very exact repro window stickers (sells them).
Naturally, you would need to be a customer (buy one) before he would release the dealer information. But he would more than likely confirm he has that dealer data beforehand of requiring payment. Since that is your main concern.
Many use his service just for the dealer info when no other free source has the data.

If you bought a PHS info packet - you can reconnect with them and ask about the dealer. Sometimes they can help, sometimes not.

Good Luck with it