At work , but just google reamers in your area, or look in the yellow pages and you will find someone that will grind any size you want. That's what I did for my Jaco rims.... they fit my Mugen axles too tight so I had a reamer made to 0.4735" to slightly enlarge the rim's axle bore.

The 4.1800mm reamer will probably just be a re-sharpened 4.2000mm. The 5.0010mm will probably be a 5.0025mm re-sharpened reamer..... that's how they re-size them sometimes- just re-sharpening them takes off a touch of material. They normally come in 0.0025mm increments.