Try Stanley Works for starters. Other than that, do other neighbors have these doors? Have they had to replace the hardware (and if so, where did they get parts)? Do you know who built the home and if the 'old man' is still around, can he tell you where he got the doors or who built them?
At some point, you may have to bite the bullet and get more modern doors. And when you do, be SURE to buy some 'extra' hardware for those parts that tend to wear out. My best to ya and hope this helps.
Jay J -Moderator
PS: Stanley sold me some hardware that wasn't meant for our particular bi-fold doors but it worked fine. Originally, the doors came with half-tracks. We wanted FULL-length tracking and they found something for us.