No, purchase of this species is illegal. You can get ahold of your local tortoise group and they will usually have contacts for torts looking for homes.....you can also contact your local humane society and get the local tortoise group number from them....
It is perfectly legal to adopt a desert tortoise from a qualified rescuer/club, but, like Angela has told you, they can't be bought, sold or taken from the wild. There is quite a hefty fine if they catch you doing so.
There are clubs and rescues in the desert tortoises' native states that have them to adopt, but the tortoises have to stay within their home state.
Also, unless you plan to have two separate habitats, you should only get one. They don't play nice (don't get along at all) and sometimes will fight to the death.