Carol,
That's a nice machine. I've seen a bunch of them on GW recently, but haven't gone for one.
Just as a thought your machine
is a rotary, so the manual you have will most likely work for it even if it is a treadle.
The head is not different, only the method of powering it.
I really don't know where to look for White manuals though.
You could try Relics {
http://www.tias.com/stores/relics/ }
or ISMACS, I don't have their link handy.
That's about all I can think of right now.
Joe