Never use your girlfriend's toys in your own ass, as that can spread some really nasty E. Coli bacteria and other pathogens.
Do buy your own toys, and ask your love to fuck you in the ass, but good. Be careful, she'll probably enjoy it, and payback is a bitch.
Good advice from Toe.
And yes..her toys are hers.
Your toys are yours, for health reasons don't mix them.
But find a good sex shop and pick up a "strap on" (fully equipped I might add).
Show it to her and tell her what you want, she how she responds, but don't push her into sometime she may be complete against.
Communication is your friend in this situation.
Love,
Liz