Most tack/feed stores will carry Brewers Yeast. I don't have a problem with any grass hay per say, they just need to be leafy not coarse. If all you can find is coarse hay (it happens some years, I expect this year to be one of them here) then feed him that but in much smaller quantities and round it out with beat pulp and a little alfalfa much like you are (you can use pellets or cubes if the hay is not available but soak them to soften them... well, with the pellets I moisten them, not soupy unless the horse knows and likes them that way or you need to increase the water intake) . I wouldn't deny him hay altogether tho, he needs the chewing and the fiber to keep his gut happy. Try spreading it out in smaller feedings so he doesn't have a lot of bulk to digest at once. As to wormer choice, it occurs to me to wonder about tape worm and if you have had a fecal count done. Perhaps before dumping a bunch of extra chemicals into a gut that already looks to be struggling with proper processing it would make sense to talk to your vet about doing a fecal test. They are as a rule pretty inexpensive and certainly better for the horse to have fewer things to upset his system if he doesn't need them. If the vet finds a heavy worm burden you can then deal with it and if not you would be glad to skip that step. Another thing you might consider (I have no experience with the product myself but others seem to have very good results) if all else seems to be unhelpful, is a product called body builder. It by all accounts will help to put weight on as muscle not fat, thus give him that 'bloom' you want to see in the ring.
