To find the bearing size measure the ID, OD and Width of the bearing. If it has metal sides it is called 'shielded' (Z or ZZ) if rubber then it is called, 'Sealed' (R or 2 RS)
ZZ shielded would mean that there are shields on both sides. 2 RS is 2 rubber seals.
Main bearing companies are SKF, FAG, RHP, INA, TIMKEN, NTN, KOYO, NSK. These are quality bearings and what you want in your transmission. Unmarked bearings are cheap, Chinese are garbage.
a 209 bearing will have an ID of 45mm, OD of 85mm and a width of 19mm.
So a 209 ZZ would have 2 metal shields. If only 1 shield is needed then you can remove the one side.
If you do not have the bearing then measure the OD of the shaft it fits on. You can then work out the bearing OD and Width by measuring where the bearing sits.
Hope this helps