Hi Jason95, and a warm welcome to the forum. grin
It's always great to have another Scott Bonnar owner on board. wink
Parts for the SB Diplomat Model 590 are very thin on the ground, however I will send you a private message (PM) I may be able to help you source the metal ring gear and pinion you require.
Just have a look for the flashing envelope next to 'My Stuff' in the top toolbar and have a look in 'My Messages'
cheers2

Please do not PM me asking for support. Please post your questions in the appropriate forums, as the replies it may receive may help all members, not just the individual member.
Kindest Regards, Darryl grin