Broken wheel on bedroom cupboard sliding door

The wheel on the lower end of the bracket (that fits into the track)is broken. The name on the back of the bracket is COX ,under this is the number21-77 and under this the numbers 21-767. The system ;track and sliding doors are part of a fitted bedroom wardrobe, installed about 26 years ago.I would be really grateful if you help me to find a replacement bracket
Thanking you
Jonathan
PS I live in England