I've accumulated quite a large number of B&S type gear cutters, and am in the process of working out which ones are duplicated. Those will be for sale for a reasonable fee, (Reasonable to me, that is ) email me if you have any specific requirements. The spare ones will go onto ebay eventually.
Phil I have a spare 20dp No4 20deg cutter, nearest I can offer. What I have done on a couple of occasions is to use a cutter that's somewhere near the right form, cut a gear with that on the mill & then use it on the hobber, with a decent amount of backlash & lots of oil, to make a proper wheel of the right form. There's not a huge loading on the wheels. I'm sure you're aware that 20dp/14.5 is plenty close enough anyway to 1.25Mod.
Another thing I did the other day was to make up a form endmill (glorified D bit really), adapting the 'two buttons' method of creating the correct form by dressing a wheel on my surface grinder to the correct radius & then carefully working out the vertical & infeeds to give a good approximation to the form on a bit of HSS .20" round. I chickened out of trying to cut the teeth with the form cutter alone, & cut the roots with a slitting saw first. The results were pretty good. I reckoned cutter wear near the tip might be a problem, but doing it this way there was no visible wear after cutting a 53 tooth wheel in mild steel. I don't claim any originality for using a vertical form cutter BTW, saw it done by John Stevenson a couple of years ago.
PS Phil - I'm short of a 2.5mm 200DA collet - do you still have any spare?