Any transformer manufacturer. I have no idea where you live so can´t recommend anything specific. Don´t forget to tell them how much current you require.
Well his information is pretty vague, but assuming 50/60Hz AC?, then a simple and cheap way would be to use two (identical) 240V to 6V transformers - put the primaries in series, and the secondaries in parallel - job done!
then a simple and cheap way would be to use two (identical) 240V to 6V transformers - put the primaries in series, and the secondaries in parallel - job done!
You ought to try it with three 1KW isolation transformers in parallel, for temporarily feeding an immersion heater - identical transformers, wired them identically - BOOM!!! - one of them was wired differently internally. Then you've got the problem of finding out which one
Easy enough with a little thought - just disconnected one end of each transformer, and measured the voltage between each of the three wires, two were 0V (near enough) the third was 480V, so flipped the connections to that one.
It was a temporary solution to my faulty immersion heater (which was leaking to earth), while I was waiting for my new central heating installation. Worked perfectly for a couple of months, and I had the transformers knocking around doing nothing anyway.