Unfortunately
If the 3 hole system is the only means of securing the blades, then you are stuck unless you can find some with the identical size and spacing. Since it's tool steel there is not easy way short of EDM, laser jet or a water jet to "drill" holes in a blank or newer longer blade.
There is another possible means of securing non original blades, called gibs, which when tightened, expand to lock the blades in place. Whether or not the cutter head has a tapered wedge shaped slot to allow this type of setup only you know. If it has a parallel slot then that won't be a safe alternative, since they can possibly fly out.
A metallurgist, machine shop, blade sharpening service, or one of our members.... would be able to tell you if the crown in the blades can be straightened by heating or bending and what effect that will have on the hardness and strength of the steel afterward.
Unfortunately....there is not a simple remedy.
I'll give you an example of fixing something that is broken.
My truck horn stopped working and the mechanic said "Your horn don't work" I said "Drop it on the ground, if it's broken, it won't be any more broken after that" He did. It worked. The point being, try anything since you have nothing to lose as long as it's safe.
:yes: bill