Terrible things that inevitably break, I agree.
I needed some temporary blinds a few years ago. Bought some doweling, calico and a few hooks.
So good there were, I thinking of contacting IKEA who could knock them out for a fiver.
Can you take some photos.
I've never heard of a blind you need to saw down to size.
There are loads of cheap identikit companies on the internet where you measure the window and it comes through the post made to size.
Blinds R us, Blind U Like. World of Blinds, Blind World etc....