I *think* that the spesh ‘stout’ hubs that came with the pitch have cartridge bearings which could be replaced, but I doubt they are intended to be user serviced, so you won’t find anyone stocking spares. You’ll need to find out the bearing codes and get them from a bearing factor.
First thing to do is (sorry if you have already done this) try tightening the bearing preload on the maxle – that is, screw the maxle in to the fork, then do up the screw on the inner axle pin which makes the QR handle harder to clamp down.
If that does nothing for it, then either mess about trying to find new bearings, or go buy a decent set of wheels. Proprietary hubs which come with fully built bikes are usually only destined to last for a year or so. I recommended Hope hoops with Stans Flow – a very good match for a pitch, and you’ll be able to take advantage of rusty mac’s advice next time you have bearing issues 🙂
Dave