You are saying it yourself: since fugu preparation is no place for DIY, you won't find general resources on how to learn to prepare it, because easily available resources would be a prompt for DIY attempts.
One needs to train under the direct supervision of a trained person
How does one obtain authorization to cook fugu?
Fugu cooking licenses are granted to those who pass a fugu handling examination, usually after having undergone apprenticeship under someone already qualified.
It should be noted that fugu cooking licenses are administered by local goverment (ie: prefectures, municipalities in the case of cities like Osaka or Kyoto), therefore the contents of the exam and the apprenticeship prior can differ from region to region. The course that one must complete can take longer in some places, while the exam can present itself to be more difficult in other areas.
For instance, in what is said the be the strictest place regarding fugu licensing in Japan: Yamaguchi Prefecture, it is necessary to work for at least 3 years under someone qualified before being allowed to take the exam, while in Tōkyō it is possible to take the test after 2 years of apprenticeship.
Also to be noted:
Fugu in the world
It is also interesting to note that Fugu dishes can also be found in South Korea, where it is called bok-eo (복어). It is also imported into the United States where it can sometimes be served under very strict regulation and licensing. Fugu is, however, entirely banned in the European Union.
To address the comments that there are videos explaining how to do it:
I am very passionate about Japan, and I have read many things related to Japanese food, including also the topic of fugu.
One of them, which I can't find back to properly quote, mentioned that the art of preparing fugu is not in removing all the toxic parts, but in doing so while leaving just enough toxin that one feels it without ending up being killed. The Japanese connoisseurs call the slight numbness which should follow eating well prepared fugu "the taste of death". Judging the amount of toxin in a fish and tune the subsequent cleaning based on that is hardly teachable in a Youtube video.