They are E13 magneto bearings. Not too hard to find in the UK, where a lot of vintage motorbikes use them. Not too sure about anywhere else. It is an old spec, and I have not been able to find a more modern equivalent which might be more widely available.
A quick look on Ebay (UK) brings up item 195980528632 from NSK, so a respectable make. ?10.56 each from Holland. Plenty more listed. Same part number works on Ebay.com, still shipped from Holland. There are several listed within the USA.
