Replacement shifter for Shimano exage 7-speed - modern shifter compatible?
For the shifter to match, you need to match the number of speeds, cassette width and shifter actuation ratio. For Shimano everything under 10 speeds (except 8-speed Dura Ace which most people don't have to care about) has the same actuation ratio, so all you need to know is the new shifters are 7-speed Shimano. These can still be bought.