The gear is part of Sony Minidisc MZ-1 loading assembly. Sony part number is 4-955-497-01 Gear (Midway C).
Replacement part was created using a semi-professional 3D printer using durable Nylon material. The gear was tested for correct operation.
You can find the gear here in schematics:
Gear is compatible with Sony Portable Minidisc Recorder MZ-1 and other minidisc devices using mechanism type MT-MZ1-106 – just check your service manual.
Pictures of the gear replacement – thanks to Stanislav!.
The gear is available in e-shop.