Thanks for that response.Presumably you've tried Indenor Retro in Germany? They have it listed at €1302 bare but there's no indication of stock level, if any.
From the picture it looks like the clamp-in injector model which some MD21Bs used - mine was (is) threaded injectors.
They are the people to contact though if you haven't already.
Indenor Retro – Die Kataloge
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