Rating of transformer of NAD 306 Amplifier

Did a quick check of NAD's website under "Where to Buy". Cut and pasted this:

India: PEERLESS FABRIKKERNE LTD./10 OCTAVES
712, Linking Rd., Bajaj Niwas
Bandra (W), Bombay India 400050
Tel: 91 22 6001047/49
Fax: 91 98215-17446
E-mail: manasr@10octaves.com

I would contact an NAD service center and discuss your situation with them. They may sell you a replacement transformer. I doubt they will supply you with any technical information and I think it would be wise to replace it with an OEM part.
You can also contact NAD but that will probably be slow going. However, they can give you a name of a service center you can contact.
What about the dealer you bought it from? They should be able to help also.