The parts manual shows part number MB500802. See www.mitsubishilinks.com for some manuals. Be sure to donate to keep them available.

https://partsouq.com/en/search/search?q=MB500802

or

https://www.ebay.com/itm/MB500802-Mitsubishi-OEM-Genuine-SLEEVE-F-BRK-CALIPER-PIN-/324304446733


Mitsu # 6 - 98 6G72 Montero Sport, Locking Rear Diff, Aisin Manual Hubs, 31x10.5

Mitsu # 7 - 02 6G74 Montero Limited