Hi there!
You should definately try to ask this same question at :
Delphi Forums / Knife 101
That "place" has what you are looking for, I am sure!
Or you could try
www.talkblade.com, another place with a whole lot of switchblade-people..
You will find lots of info on both vintage, contemporary, US and Italian automatic knives on the mentioned sites.
And off course,
www.billdeshivs.com - start there by the way!!!
I am SURE that I have read somewhere that springs for those older American switchblades do exist - so keep looking and I think you will find what you need!!!
GOOD LUCK!
Martin