I've wondered about this. Assuming our suppliers are predominately private companies, we don't know their numbers. A google produced this:
https://www.grandviewresearch.com/industry-analysis/adult-diapers-market
It cites alternate diaper applications, "guards on long duties who are not...
I got a measuring tape, put on my diapers, and took all these measurements:
https://i.etsystatic.com/5263524/r/il/2d817f/1220694460/il_570xN.1220694460_38fk.jpg
From these you should be able to order anything almost perfectly.
Another shout-out for Baby Pants onsies! I wear one every day.
I've found that people will not notice that I'm wearing my baby clothes (diapers, plastic-pants, and onesie) underneath my big-boy clothes.
Okay, this may be strange, but I NEVER wet or mess in my diaper. I tried it and found it revolting. I just love the soft feeling of a clean, thick diaper.