The door trucks are available from FP Marine.
Note, there are three sizes (heights), 23mm, 25mm and 31mm. The replacement MUST match the original.
https://www.fpmarine.com/Sliding-door-track-rollers-p/door%20truck%20a%2023mm.htm
FYI, my doors uses two different sizes of trucks.
It is good to keep this area clean. I use my vacuum followed by a garden hose to ensure crud doesn't accumulate in the tracks or the truck bearings.
Note that the tracks can also wear and deteriorate. FP Marine also sells that material. My experience is that I have replaced several trucks over the decades, but am still using the original tracks. The tracks still look new.
