I grow my own trays of grass, for the bunnies. It is very easy and doesn't take long to do, The Hay Experts sell kits.
You could try reducing his number of pellets and giving him a variety of different types of hay/grass (you can get taster packs), he may surprise you.
My lot like hay but I mix lots of other stuff into it for variety. Pampered Piggies sell lots of dried leaves that seem to be a hit with my two. I think you just have to keep trying stuff, although all rabbits have their preferences.