Ken,
For the slide plate try Thayer Rags parts: {
http://thayerrags.com/ } I've gotten some parts from him for my DRESSMASTER.
I have a downloaded owners manual for the 127 series White made machines on my thumb drive. I do not know where I found it. If you can't find one I'd be glad to try and email the file to you. Hopefully my machine would cooperate.
Now some tips.
Your machine rotates opposite Singers, IE the hand wheels rotates clockwise, not counter clockwise.
It uses regular White-Kenmore bobbins.
It uses regular 15x1 needles.
Use petroleum jelly as lube in the motor grease tubes. Or the old Singer motor lube in the tube if you have some.
Cord sets and bobbins can be bought from Sew-Classic {
http://www.shop.sew-classic.com/ }
I also suggest Tri-Flow oil. It is superior to regular sewing machine oil. You can get it at Sew-Classic, bicycle shops, and some hardware stores.
These White made machines are some of the best straight stitch machines you can use.
Joe