If you want to sell through a retail store, you'll need to come up with a business plan (even if you're only asking the store to hold them on consignment).
Start by thinking about the mission for your business. What makes your cards so special compared to every other card on the market? Why should a store choose to sell your cards over someone else's? Keep in mind that by selling your cards, a store will be taking shelf space away from another merchant. You need to differentiate yourself.
Make sure that the store understands what you'll need in terms of shelf space, and make sure you can justify it: How much space do you need, what will your display look like, why is such a display right for the store.
Finally, you need to give them some sales forecasts. How many sales do you predict you'll make in a given period, how much revenue will this generate, and what kind of a cut will the retail store get out of this.
You can't pull these numbers out of a hat: you need to do market research. This doesn't need to be difficult - just get a sense of how willing the general public is to buy your cards. Have you ever tried selling them at a bazaar or craft fair? If you can tell a retail merchant about a really successful experience that you had at a trade fair (such as selling more than any other artisan, or something else), this can be just as convincing as having piles of market data.
Just bear in mind that it's a cruel world out there, and just because friends and family love your cards, it doesn't mean that the rest of the martket will be as welcoming.
Also, remember that retail stores and the Internet are not the only mediums for selling items. What about altering your business model, and offering custom-made cards for businesses who need bulk orders (especially at Christmas time)? Or, focusing on making thank-you cards and invitations (which are much more versatile and are frequently used by the business market compared to greeting cards, which are really only used at Christmas)?
Start small. If you have a product that people want, then they'll come to you, and it will sell itself! Good luck!