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O wow. Then I think you're golden : -)
Recently I printed a new set of keytops for a Speedline - have a look at
Making STL partfiles for concave discs should be fairly easy (if have dimensions, can help you with that). Using 3DHubs.com then the trick will be to find a hub with low cost for many small identical parts.
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I have an Underwood Noiseless with very similar keys, shift lock, backspace and a few others though are green. Appears to be some kind of hardened rubber. If you could use the keys let me know.
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Sorry, should have updated this thread—a local repairman had a set of spares, so I used those. Thanks though!