In the series 3 episode, Smith and Jones, The Doctor gets a new sonic birador at the end. Where did that come from? Does he have a stash of them on the TARDIS?

I dont know about the tenth doctors tardis, but on the adventure games (Featuring the 11th) He has a matter recombulator or somthing that can create divices such as sonic screwdrivers. Even if he dosent have one of these, hes a time traveler. He could just pick one up in the future than go back and say hi to martha.