We would face almost the same scenario shipped from Europe to the US, maybe reach out to the European owners on the Facebook De Tomaso parts groups?
There is also a reputable ZF rebuilder in the UK by name of Paul Fleming, maybe he carries spares or has access to an R&P duty paid if you are quick before Brexit!
Paul Fleming
Maldon, Essex
e-mail: paul@flemingpaul.wanadoo.co.uk
Mobile: 07710 77867