Info on transformers? Where to find?
You've got it right. Many (though by no means all) power supply magnetics are custom parts. Your best bet is to try to find the manufacturer of the transformer and see if they list the part on their website. You could also contact them and ask. But odds are a custom magnetics manufacturer won't hand out information about their customers' proprietary designs. This is especially true if the magnetics manufacturer is also the power supply manufacturer.

I'm afraid if you want to understand that transformer, you'll have to take it out and analyze it.