Old Bay Seasoning can be purchased at most grocery stores.
Here is an untried copycat recipe for the mixture.
I use the real stuff in macaroni and potato salads.

Exported from MasterCook II *

Old Bay Seasoning

Recipe By :
Serving Size : 1 Preparation Time :0:00
Categories : Mixes Copycat

Amount Measure Ingredient -- Preparation Method
-------- ------------ --------------------------------
1 Tbsp Celery Seed
1 Tbsp Whole Black Peppercorns
6 Bay Leaves
1/2 Tsp Whole Cardamom
1/2 Tsp Mustard Seed
4 Whole Cloves
1 Tsp Sweet Hungarian Paprika
1/4 Tsp Mace

In a spice grinder or small food processor, combine all of the
ingredients. Grind well and store in a small glass jar.

>From "Sundays at the Moosewood Restaurant"

Also, if you want to order, here's the address of the company:
Old Bay Company, Inc., P. O. Box 1802, Baltimore Maryland 21203-1802