You can get any size bearing on ebay.
However, if you look closely, more often than not the bearing part number is stamped on the side shield*
Say for example the bearing is 6808-2RS. 6808 is the bearing size, so the inside,outside and thickness sizes will always be the same for any 6808 bearing and the '2RS' stands for 2 rubber shields. -those are the black bits on the outside that keeps dust/water etc out of the greasy inners.
Take some measurements off the bearing you have - then check here.
https://www.axminstertools.com/bearings-ax452315
I dont know the quality of the bearings Axminster uses, but I would expect them to be reasonable quality. Avoid cheap, cheap is bad. usually poor tolerances, little to no grease and they can seize up or fall apart.
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Much cheaper that way