Can't find correctly sized gear

[ollien]

In order to fix our intake, we've opted to change to a P60 Gearbox instead of PG27. However, our current gear setup uses these two gears. The big issue we're facing is that we either need to replace that first gear with something that can fit a P60 and a correctly sized machine key, or find a new combination of gears that can do the same thing and hold our hex shaft. I've also tried finding alternate shafts for the P60 that would work with the current gear setup but to no avail.

Could someone help me find some gears or a new shaft?

EDIT: For reference, A P60 has a 1/2 inch shaft and an 1/8th inch keyway.