For replacement masts you might want to talk to Lift Tech in South Carolina or Manitou North America in Waco, Texas. You will need have the Make, Model & Serial Number of the unit so they will be able to determine if they have the info to develop the axle & tilt cylinder brackets & the lift line (mast to control valve) connection.
Not aware of a mast rebuilder other than the authorized dealer for the truck brand.
If you are an end user you might not have any luck.
Do a google search to get contact information.
GL
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