They are standard medium duty deep groove ball bearings that you can get from any bearing shop ( best price )
Most engineering supply shops
Most auto parts stores with sales staff who can find a part without a computer
Dont know about US hardwear stores.
Jacks Small Engines sells the bearings good price good service but you will have to look up the parts diagrams ( on the web site ) to find the actual part number.
Never buy bearings on line from evilbay, craigs or amazon.
There are more fake bearings out there than real ones and the bearing fakers will put any name on the bearings that the sharletons ask for.
In the US you should be looking about $ 5 to $ 10 each for the bearings so worth doing comparred to $ 60 - $ 140 for the complete mandrel.