[Zero10]

The easiest thing to do is check the brand of the panel, and whether it is a full-height or half-height breaker, and whether it is packaged with other breakers.
Siemens likes to make 4-packs of half-size breakers with twin-pole breakers in the middle.
Things like that are important. The actual numbers off of the breaker are not as important.

I'd expect just about any home depot will carry the breaker you are looking for. Expect ~$25-$40 for a 2-pole 30A breaker (dryer should be a 30A circuit).
I wouldn't worry about tracking one down before you go back there. Go in, remove the old breaker and take it to Home Depot or the electrical store of your choice.

On a related topic, what do you mean the breaker is going bad?.... Nuissance tripping? Not tripping?....