Mike Mayberry of Mayberry Lincoln-Mercury in CA acquired a load of ZF spares recently (his username is 'King' on this forum).
You can probably get away with a used Ring & Pinion.
Other good sources are;
RBT direct
Dennis Quella at Pantera Performance Center, Colorado
Once you have spares pricing you might want to evaluate cost of a replacement ZF vs. rebuilding yours. I have a used (previously rebuilt) one for sale at US$6500.
Julian
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