Want to get a new power brake booster, 1973 Duster.

Yes, everybody seems to be out.
You can order w rebuild kit and do it yourself following the instructions in the FSM.
For example:
https://www.parts123.com/parts123/y...~S7180UIHMG16618120930b~Z5Z5Z5~Z5Z5Z50001029z
Contact them to confirm this is the correct kit.
Alternatively, you can send it out to have it rebuilt.
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