The author mentions that locating metric fasteners in bulk may be a problem.

When I need anything metric (automobiles use a lot of metric fasteners of various sizes) I order them from BelMetric.com [0].

You can order one or one hundred or one thousand and they assemble your order and get it out to you faster than any other provider of fasteners that I have used.

They have an excellent selection including specialty parts that might be useful for building telescopes.

https://belmetric.com/

They're the best.

Overall this looks like an interesting project that is not difficult to make. I may need to level my printer bed and see what happens.