The easiest way to get your own deck is to, of course, be famous. The companies will salivate at the thought of a celebrity endorsement. Do you think David Copperfield has to pay for decks of cards?
Make a video of yourself. This is not a dating service video, but rather a montage of your magic skills.
Send the video to card companies like AdMagic and explain that you perform a lot and would like your own deck of cards.
Let them know that you will use their cards and promote them heavily if you can get some sort of discount.
Come up with the design that best fits your taste and style. A family magician should not have a deck with knives or guns or anything else along those lines, for instance.
Fill out the necessary paperwork CORRECTLY and be sure to follow through on your promotional promise.
Before any of this, decide if you really deserve your own deck. Usually only the big dogs have their own decks and it is a sign of status in the magic community.