1966 Dart speedometer - DIY fix possible?

My speedometer is not working, so I picked up a spare 1966 Dart cluster. Only to find it's not working either. I tore it apart and found the problem seems to be this plastic rivet that holds the spring bracket in place - it's broken and the bracket spins freely.

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Any idea where I could source replacements, or how to get the spring adjusted once I can find one?