My son has a chinese 90 quad. It has no spark does anyone know where i can get it repaired?

if you are in sd there is a place called cheap thrills in lemon grove

Any shop shoul dbe able to work on it. Probably something simple.
Where are you?

Not every shop can get parts though, that is the problem. Your best bet is taking it to a shop that sells and services them.

Fireball is right, it's better to take it to a shop that sells them, reason being is they should have a spare around to take a part off to see it that fixes it. That will save you lots of time and more so money.
good luck.