If you happen to be in the Akihabara district in Tokyo, one place worthy of a visit may be
Noguchi Transformer ("Noguchi Toransu" in Japanese).
They stock and sell many retail models of Tango, Tamura, Hashimoto, and their own brand power and output transformers and chokes.
They are located 3 minutes walk from the JR Akihabara station in the basement level of a nondescript, skinny building by the name of
"Tokyo Radio Department Store" ("Tokyo Radio Departo" in Japanese).
JR Akihabara Station -
"Electric Town" entrance:
Entrance to "Radio Departo":
The first sight of Noguchi Transformer that will greet you as you arrive on the basement floor on the escalator is the "show wall (not a room, but a wall)" of audio equipment showcasing some of their inductor products:
This version of Nipper looks away, in mild disgust, from "His Master's Vice" (Reminded me of my better half...):
An "expert's implementation" of an amplifier construction article in a magazine:
"Lookie but no touchy" (especially with live 800V AC):
300B Single Stereo Amplifier (I think...):
A magazine article on EL84 push-pull stereo amplifier, and the pre-punched chassis for the construction article for sale:
More amplifiers that use their products:
Here are some of the Noguchi products:
You can buy many of the name brand transformers "over the counter":
Or "off the shelf":
Or "out of the show case":
Noguchi's own FINEMET "C-Core" single output transformers - 5k/7K Primary, 4-8-16 ohm secondary, 3 Watts - costs a tidy 1,3500 Yen ($167 US) each:
I would not go there if you are merely looking for low prices, however.