Did you get the problem sorted?
9 times out of 10 a wheel wobble is wheel and tyre related, some tyre shops will be good and tell you if there is a problem, others won't.
Causes can include (but are not limited to)
- Wheels bent
- Old tyres
- Tyres not round (also see: cheap tyres)
- Tyres unevenly worn
Do you have half decent tyres on the car? How old are your tyres? Have you tried rotating wheels front to back? (if a wheel is slightly bent, it's better to have it on the back).
The other 10% of the time as Ravi said it could be related to other parts of the steering/suspension.