GO to the Oregan, Prime Line, Rotary , Stens web catalogues
All of them have tables of blades by length
All of these list the type & size of the centre hole
So any blade with the same length & centre hole can be fitted.
Weather they will work well with your deck will be a trial & error job for you
I regularly use different mower blades because they suit the customers needs
And yes you can cut down any blade but you must pay close attention to the blade balance
I just fitted a later model0 30" blade to an old Murray but had to take 2mm of each end .
THe original blade is currently out of stock & $ 195
The latter blade is readily available & $ 65
