Where can I get the correct runner wheels for my shower door?

I have a curved sliding shower door. The bottom runners wore out and I replaced them with what looked like the same runners. There is not enough adjustment to lift the wheels into the lower runner groove and consequently the wheels just rest on the bottom of the guides and do not retain the door firmly in position.
If you push the door inwards it swings from the top rollers and is quite dangerous. Are there any fittings that will adjust to lift the wheels up into the runner guides?