Shower BiFold Door Track

I have a bi-fold door on an en-suite shower which has had problems since we moved into the property. In the last few days the track wheels for this door have completely failed and disintegrated, causing the doors to depart their frame.
Can anyone advise a source for parts for the bi-fold door track, or a source for complete replacement tracks?
It seems a shame to pay 120 to 200 for a complete replacement door when the existing glass panels are undamaged and apparently still fit for use.
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