This is like complaining I can't find a body panels or a swingarm wrench or a hydraulic clutch lever for a 1980 Honda VFR even in Japan.
You think we are making modern drills with the same collection of parts out of your antique? We just figured out a better way to put them all together?
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I vaguely recall bsfeechannel mentioned this was a ball bearing? This is actually something which makes sense to standardize. Ball bearings have insane tolerances and a very complex and sophisticated manufacturing method, and getting all the pieces of this process in harmony is a bear. And we don't really need otherwise identical ball bearings with OD in imperial and in metric.
In US, we use metric ball bearings pretty much, like everyone else, unless there's a really really good reason. Your old drill is a victim of metrication. Or of standardization in general.
A ball bearing manufacturer can stop his production line and tweak everything to churn out imperial sized bearings, but of course that costs a crapton. And why not crank out 1000 rather than just the one, after you've done all that and done all the tweaking and tuning and making dozens of pieces of scrap before they start coming out in spec (in the time they could have continued to churn out hundreds or thousands of the metric ones with a blindfold on; just another Wednesday). And then they have to tweak everything back after they make your stupid bearing.
An American restoring your drill would have figure out how to use the next closest size, by reaming out the hole bigger, or by machining a bushing to make the smaller one fit. Or maybe both. Reaming it out so you can make a bushing that isn't wafer thin. OTOH, if the hole is just a tad too big, you might even be able to press fit it in with just some shim stock strategically shoved between? Maybe a trick you can try if you don't have fancy tools and skills. Ditto to the shaft that goes in it, of course. Might need a bushing or building up and/or turning down.
You could probably buy bushings or shims for some of these problems. If you sat down and did some math to know how to find it. Rather than just trying to order the numbers on the part.