Right, we can get very little from what you said so far. Has it been printed already? How many copies have been made? How is it packaged? What's the theme, if it has one? Knowing these things can help people give advice.
Many artist produced decks sell by word of mouth & never hit the stores at all. The artist would most likely post pictures up online, put out messages on tarot bulletin boards, have a copy sent for review to a few places online, and sell their decks that way.
If the deck is finished, the artist can also try to contact US Games and Llewellyn and see if they're interested--follow the format they give on their sites as to how to present the project (some want it on CD, with a cover letter, and a sample card, etc.) You can also check with smaller publishers like Bear Company. There's a list somewhere on the Deck Creation archives.
If the bookstores are going to carry it, the deck has to be in a box with an ISBN number, or they can't order it (warehouses are set up this way now, items without the ISBN number just can't get into their ordering system for stocking the larger chain stores). Smaller bookstores that are independantly owned, new age stores, etc. can be contacted separately & queried. But for display of the deck, it would have to have a nice looking box to interest the customer (and to sit properly on the shelf at the store without getting damaged).
There are other things to try, like contacting AzureGreen (or is it AzureBlue?) which is a metaphysical clearing house sort of, on the internet. Or eBay sales. Or selling it at a table at the local science fiction conventions, spirit fairs & SCA events.
