Bicycles have used cup and cone bearings in rotating parts for generations. Nowadays many parts are replacing them with sealed bearings, which are less servicable but entirely replaceable. Cup and cone bearings are easily maintained, but if parts wear out can be difficult to replace.
Maintenance
Fresh bearings are packed with grease, but over time moisture and grit can work it's way in. Bottom brackets and wheels can pick up serious dirt that can increase wear on bearings and races. Service bearings periodically to clean out dirt and replace fresh grease.
Replacement wheel parts
Cones, which thread onto the axle, can become pitted and will need to be replaced. Keeping bearings cleaned and greased is the best way to avoid this. Also, avoid hard impacts like going off curbs.
Shimano sells replacement packages with an axle, bearings, cones, and washers. Check the service manual for compatible parts. You may have to go searching for rare parts.
Wheels Manufacturing sells generic parts and may have a suitable replacements.