Hey sunsatellite -- I've got some good news and I've got some bad news. Bad news first: folks who are under 18 cannot legally purchase sex toys, and I'm pretty sure this might extend to using a parent's credit card to do so even if you're pretty sure your mom would be okay with the purchase generally speaking. I'm leaving a note for my colleagues to chime in if I'm wrong and answer your initial question about sites if we can.
Good news is, because you're interested in a vibrator for clitoral stimulation primarily, you may be able to obtain something legally that can be used as a vibrator, like a regular ol' muscle massager. You can buy them at a variety of stores. I've seen them at Target, Walmart, and Brookstone pretty regularly. The chances of you being able to find something affordable at one of those places and walk out of the store with it yourself are pretty high. One thing to note with those options is that they are typically not waterproof or made of a material that can be cleaned the same way sex toys typically are, if that matters to you. To be honest, anything that produces a vibrating sensation can be used for masturbatory purposes, just make sure it's not sharp anywhere and can't electrocute you. Our resource
D.I.Y. Sex Toys: Self-Love Edition has quite a few suggestions that you may already have around your home.