Being easy to do and getting it validated by authorities are two different things.
What gave you the idea that they going to pay any attention to that? When did they start inspecting brakes or even checking to see if brakes existed, on little single axle trailers? There is no validation by authorities for that sort of thing. They don't check.
It might happen if there is an accident review. Some times lawyers like to get involved.
I guess I was just brought up wrong and taught to follow the law.
I'm not advocating violating the law. In all of the states where I've had trailers registered(three of them, including VA), the only information that the state wants about small trailers is the empty weight and the color. That's it. They don't ask about or check for brakes and they certainly don't have any objection to you installing brakes on a trailer that didn't originally have them. All I'm suggesting here is that you don't need to find a manufacturer that will install brakes on a trailer. You can do it yourself in an hour or so. There's nothing about that that violates any law and there's nothing about the manufacturer installing the brakes that would change anything, legally.
What might happen? The law does not specify who can legally install brakes on a trailer. Do you really think a court is going to have a problem with someone installing brakes on a trailer that didn't have them?
