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Just thought i'd chip in here as i'm in the UK also. I found they were easily available in the UK but extremely expensive for a few bearings so i ended up getting them off ebay in the US which was then fulfilled from china to keep the costs manageable. I think it's an excellent design and really appreciate you putting up the design for free but i think you would get a lot more people making this if it were more standard/cheaper bearings.
Again not knocking you at all and see why you did the design this way but i think people would be more than happy to print with some support and work on the 3d print that way if it kept the costs much lower.