Many well known chefs have a Cajun spice blend on the market as well as do most large spice companies. I happen to like this one that I picked up at a flee market.
My philosophy for buying spices is to purchase small quantities from the large bulk spice jars in the store where I like to shop. I usually look for the jar that is just opened and take just enough of the fresh spice to last a couple of weeks. I always seem to have dozens of little packets of unlabeled spices, as seen in the photo, stuffed into my spice cabinet. Funny enough, sometimes I will decide to prepare a dish just because they put a new jar of a certain spice on the shelf that day.
Be sure to cook your spices. Spices are well know as breeding grounds for bacteria. The germs can come from birds flying over them as the grow or from chefs sticking their dirty fingers into the spices. I personally have no problem with irradiated spices for this reason and am not exactly sure what to think about organic spices.
