Actually, tempered glass can not be cut.
tempered glass is used for the side windows on modern cars. when broken it shatters into hundreds of small pieces which is acceptable for side windows but obviously would cause major issues if a windshield were to shatter into thousands of pieces
safety laminated glass is used for the windshield and safety laminated glass can be cut using the proper technique
finding a correctly curved tempered side window on a modern car will be of no value, as it can not be cut and resized
I understand this modification has been done on a few cars. And you are correct, it will require an expensive, custom made, to your precise template, one piece glass.
Larry