I've looked at similar questions to this and the only shifter that is brought up is the Shimano Alfine SL-S503 8-speed shifter. Are there any other compatible shifters (preferably trigger-shifters)?
Shimano internal gear hubs require their own shifters. They are not compatible with derailleur shifters.
According to the 2017-18 line up chart, the SL-S503 trigger or SL-C6000-8 'gripshifters' are your only choices.