I posted this in your other thread so thought I would copy it here.
You can buy blank gears from HPC.If you`re replacing a gear with a splined bore.Turn the old gear down and use what`s left as a bush for the new gear.
You can make gears on the mill quite easily with an involute cutter and your dividing head.
Or you could ask John Stevenson to cut one for you or just for advice.John knows his gears and loads of different ways to do them.
Looking at the picture you only seem to need three gears,or is there more welded than the one I can see?
Edit:Now I seen this pic I think you need more than three gears.