Prototype – available for testing only.
Gear attached to the motor – part of Sony X-3356-638-1 Motor (Reel R) Assembly. Gear is also compatible with Sony X-3371-429-1 that is actualy a substitute part.
X-3356-638-1 Motor (Reel R) Assy Gear 
X-3356-638-1 Replacement Part
3D printed replacement part was created according to the original part but it was not fully tested yet.
Anybody who is interested in testing and helping to finish the design is welcome. I can send the prototype for this purpose.
The part is compatible with following devices:
TCKA2E, TCKA2ES, TCKA2ESU, TCK620, TCK850, TCK850ES, TCRX79ES, TCWR901ES, TCWR99ES.
It also might be part of other device – just check corresponding service manual.