Changing SRAM Apex brifters to flat bar - which is it possible to get hydraulic brake levers and trigger shifters to match?
The SRAM Apex line includes flat bar trigger shifters. 

I don't think there are flat bar brake levers compatible with Apex hydraulic calipers, so you'd be looking at getting separate MTB levers and calipers. SRAM MTB and Road levers and calipers are not compatible with each other - see this answer.