Canon A550 and A560 have the same body and most of the internal parts, including lens assembly are the same. Canon won't sell individual parts within the lens assembly. There could be two possiblities. One is (unlikely) that the lens assembly components have been knocked off from their position. The other is that because of a knock, or dropping the camera, the gears in the gearbox of the lens assembly are broken. These gears are the same as the ones in A530/A540, and are available from ebay for $12.50 including shipping. Checkout my site for how to open up the camera and the lens assembly to replace these:
For A550 and A560, if you take it to the professional repair shop, it might not be cost effective, since it might cost around $90. Canon does not sell gears, so they might have to replace the entire lens assembly. The new camera is available these days for around $140.