HOG is only sort of DIY friendly:
HOG does not widely promote self-service, they do, however, offer a course that non-shop techs can take to become "certified" to work on their own HOG regulators. They are quite strict on having the "proper" tools on-hand to work on the regs including a magnehelic gauge.
Why HOG is often mistaken for being more widely DIY friendly is because they do not restrict their dealers from selling service kits to the public, like most of the major brands do. If a shop selling their equipment decides that one should be "certified" to work on HOG regulators prior to them selling service kits to customers, HOG would contend that this is an issue between the shop and the customer. I am not 100%, but pretty sure, that Divers Supply down in Georgia (which either owns or is owned by Edge-HOG) does not sell service kits for HOG regulators unless the person has taken the maintenance course, I do not see kits for sale on their website. But, Dive Rite In Scuba (DRIS) sells HOG regulator service kits in-store and on their website.
So, yes, one can obtain service kits and perhaps parts if a shop is willing to sell them to you, but only as function of Edge-HOG not restricting their dealers/vendors from selling them.
Again I am not 100%, but it is also my understanding that Deep6 used to openly sell their regulator service kits but in the past few years began restricting sales to those who have taken their regulator maintenance course.
I have been told by a source inside the company that the reason why the service manual(s) are not made available is due to an insurance policy issue for Edge-HOG. Their insurance provider will not allow them to publicly publish the manuals. They provide access to those who have passed their course and ask that those who have access to not share them with those who have not taken the course.
-Z