I recall reading one site that purported to sell these gears, but don't recall at all what it might have been. These gears are notoriously hard to buy unless you have a speedometer repair shop.

Years ago I made one for a SAAB (which also has a VDO gauge). I used modeling clay to make a mold from the old gear and polyester resin to make a new one. It worked for years before the car was finally rear-ended.