Yeah, B & K are very proud of the prices they get for repair parts.
If you have the original gears, here's what I would do. Measure the OD with mics. Take this measurement and divide it into the number of teeth. This should give you the diametrical pitch of the gear. I'm guessing 16 DP for smaller Sheldon lathes. And I believe they are all 20 deg. pressure angle.
Next would be to start looking for stock gears with the number of teeth and diametrical pitch and 20 degree pressure angle. Don't worry about the bore or the thickness. Those will have to modified to fit your lathe.
Last, if any one of these gears were of the fibered material, Micarta, you will either have to make the gear yourself or get some one to make the gear for you.
Ken
BTW- have you tried to post a message over on the Sheldon Lathe group on Yahoo? There may be someone that is willing to help you on making gears for you. These gears rarely come up for sale. Most of the time they are damaged beyond repair. And that reminds me, if there is only one or two teeth missing, I would suggest brazing up the area and cut new gear teeth. Of course, this may be possible if you don't have a mill.