This is really a case of pay your money and take your chances.
Bearings is one of those things that there is a huge price difference between top shelf quality and mainland chines imports.
For example folger tech sells what you are asking for. At very reasonable prices $3 usd each . but you may need to buy a couple extras and sort though for the best.
Mcmaster Carr known for top shelf industrial products sells them as well for $45 each a bit pricey for a home built printer.
Misumi USA seems to be the best value for linear motion products.
http://us.misumi-ec.com/
Seems a bit tricky to find pricing.
this commentary may help bottom line is chinese bearing work if you are willing to sort though a few.
https://www.youtube.com/watch?v=5Dkruh8NO9E
Hope this helps
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