When I was an assistant manager at a print shop, there was a company called Rushgears that used to send me books of gears that they could make. I see they still have a website. You can send them your gears, and they can re-create them for you, but you'd better brace yourself for the price. Maybe someone with deep pockets would order enough to bring down the unit cost. I'm still looking for the Cub Cadet fanatic with deep pockets to buy a certain NOS item I have, so we may be waiting a while.
Yes, there are custom or specialty gear mfg companies around. My first salaried job at IH's FARMALL PLANT was a production schedulers job in a gear machining dept. My dept did special secondary machining to gears, gear "Shaving", chamfered gear tooth edges to ease engagement, milling oil grooves in faces of gears, drilling oil holes. Plus I had 2 guys on 1st shift and 2 more on 2nd shift that ran a Leihbehr Hob and Red Ring gear shaver cell, each guy ran a hob and a shaver. My job was to chase enough machined gear blanks out of other departments to keep these 4 guys busy. It was piecework, their pay was directly tied to how many pieces of each gear they got off each machine. They were 4 of the highest paid guys in the whole shop. The FARMALL PLANT was reported to be the largest gear machining plant in the country, they made bull gears and the matching pinions, all the speed and range transmission gears, and gears for other IH plants like I.H. East Moline combine plant, IH Geelong, Australia, they built lots of ag tractors there. Eventually IH Louisville tooled up to machine the gear blank forgings they made for FARMALL, and we started getting ready to assemble gears and shafts daily from LVL.
There are lots of companies that make custom gears. An internet search will show hundreds, probably thousands of companies. The creeper gears are really simple in design. I suspect they are machined out of barstock, not a forging or a casting. At a company I worked at after FARMALL, WE had outsourced machining on very large cast steel gear blanks making them into a herringbone style gear, gear teeth in a "V" across the surface of the gear, and it's matching drive pinion. The shop was ASTRON GEAR in Chicago, Illinois. Very good shop, but there's many others. That was 25, almost 30 years ago, they "Might" still be in business.
A other possibility is I'm pretty sure then creeper drive uses straight cut spur gears. Lots of tool & die shops have Mitsubishi Wire EDM machines, Electric Discharge Machining, a very precise method, great accuracy, able to cut hardened steels without effecting the heat treatment. EDM isn't cheap but straight cut spur gears can be cut in "stacks" reducing time and therefore cost. I think the "as cut" surface finish is good enough to run.
We had a row of about a dozen Barber-Coleman hobs of different sizes that cut teeth on gear blanks made by IHC West Pullman PLANT, they were pump gears used in engine oil pumps, hydraulic oil pumps, and lube oil pumps for transmissions. 2-3 guys ran ALL those hobs, think they ran 2 shifts.
If you can get hold of an underdrive with good gears and create a drawing of the gears, diameter, width, center bore diameter, keyway width & depth, all those can be measured off a good used gear, but things like "Pressure Angle", "pitch diameter" and specs for proper involute tooth profile, that's what the gear shavers created on the teeth, in the case of the creeper, the involute helps hold the creeper stay engaged in gear.
I don't know how hard it would be to find a Danco creeper drive blue print, but ALL those specs would be on a print. OR, Julian Stahl at Midwest SuperCub could probably tell you, he makes various sizes of primary reduction gears for gear drive Cubbies.