Those gears are sold by the same company that has powdered unicorn horn and bottled moonbeams. They just don't exist. A complete center section from a HO 72 axle from the late 1960's- - - -early 70's will bolt in, with a 4.10:1 ratio, but those things are also very scarce. That's probably because a lot of us dirt track racers scavenged them up and wore them out in the 1980's.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!