I stumbled onto these which may or may not work with the Tamyia Double Gearbox. They come from the same family of motors. They are the same physical size as the original.
1.5-3VDCMiniature Motors 6600-8800 RPM 15x20mm x 25mm long 230-710mADC 3-pole Permanent Magnet 2mm dia shaft SPEC=FA-130RA typically used in razors tools instruments & toys 2/$1.00 Sppec's avail. "Call for Sale Price 1K@$0.333 Each."