Axle Bearing two questions

Hello all,
I have two questions. We have recently acquired a second additional kart. This new kart has rear 50mm axle bearings that seems to be very spinny and when you turn the axle they spin really well. The bearing has the number 58210ZZC4 on one side and GBI on the other. I’m liking this bearing and was looking to see where I could find them?
second question:
On our other kart we just bought some 50mm bearings from CometKartSales and installed them. They are not very spinny and actually my older bearings seemed to spin better( I have no chain or anything attached. Just the axle inside the bearings and on the frame). Is there a break-in period for axle bearings and what is the best way to break them in?? Just time or is there something magical I should be doing?

Thank you guys so much.

A new bearing is not going to spin as easily as an older one because it’s packed with grease. It will free up on its own with use or you can speed up the process with a spray lubricant such as Tri-flow.

It’s actually a SB210ZZ and C4 is the internal clearance. You will notice that the shield doesn’t contact the inner raceway which makes the bearing free spinning. Give your new ones a good spray between shield and raceway with a good lubricant and they should free up with more use.