A quick search seems to suggest the Shimano Ultegra 8 speed barends have been discontinued, which are the levers i would have suggested - i bought a pair just a couple years ago and assumed they were still available.
Looks like Microshift makes a Shimano compatible set which would work for you. They were the only one i was seeing on searches for indexed 8-speed that are currently being produced. You could check ebay and maybe score a used set of Shimano on the cheap - they are pretty indestructible.

As for the brake levers, the Tektro RL520 are the long pull drop bar brake levers, and should work with your M280 calipers.