They are most likely something custom made. It's not like there is a drought of high-end transformer manufacturers in Japan. Hashimoto, Tango, Tamura are the high end candidates but they likely used something more basic. If you want to go custom then why not contact Electraprint? Kabeer ordered from them and for 10W units they are huge. To find the correct values to get a quate take an 8 ohm input, multiply it by the desired ratio and square it to find the impedance of the secondary. Stax used 1:25 transformers but less then that would also work.