Wondering Where to Buy Some Gadgets for Telescopes

My son just turned ten. For Christmas last year, Santa brought him a telescope. It was exactly what he wanted - at the time. Since then he has learned a bit more about outer space and wants to see even more of it. I do not want to have to invest in a new telescope, so instead I have been wondering where to buy telescope accessories. I have read that a few add ons might help to get his telescope to do all of the things that he now wants it to do, and that would save me money as well!