3/4" Rear Sprocket Adapter?

[Brokenjack]

I just traded a couple of trash bikes for a Murray Ultra Terrain Extreme bike. The diameter of the rear wheel hub is 3/4". I see commonly available rear sprocket adapters in 1" as the smallest. Do the 3/4" adapters exist?
Thanks

 

[MotoMagz]

Maniac Mechanic makes custom parts. Besides him making a custom adapter could use a correct spacer.