I would agree with that, even though CBs are actually still amazingly common. It's estimated that about half of long-haul truckers still have them and they are still very popular with off-road groups and in rural areas. But the need for working on them is all-but gone. With relatively few exceptions, modern CBs are cheap enough that the cost to repair would likely be more than the cost to replace, plus, like most electronics, they are so highly integrated that there isn't that much to repair to begin with. Older, premium radios are still out there, but that is such a niche market that it's unlikely to be a money-maker for someone just getting into it.So exactly what do you want to be taught, and then what do you plan to do with that knowledge?
There is not much need for someone to work on CB radios.