Shifters now that they are unavailable what can I use?
You do not need replacement combined shifter and brake units. Those were popular at one time but separate units are the norm now.

So you have two separate issues: Finding compatible brake levers and finding compatible shifters.

As other have said you need V-brake compatible levers for mechanical disc brakes. This should give you a wide choice and the ability to find 4-finger levers.

Literally any Shimano 3x8 shifters will work with your existing derailleurs. The expected sprocket spacing and derailleur actuation ratio (ratio of length of cage pulled to lateral movement of the cage) has remained constant for Shimano MTB drivetrains at 9 rear speeds or less. It would be nice to upgrade from the EF51 shifters but Unfortunately Shimano now only makes 3x8 shifters for their lowest level groupsets, but searching on Ebay might net you some earlier but higher level items.