So my brother was riding his YFZ450 and dropped 2 valves and he says the whole cylinder head is non repairable (which I find hard to believe) anyone know a good place to send the cylinder head assembly to get rebuilt?

I dont know of a good place, but Ive seen a 400ex head where they only dropped one valve and I dont think Id run it again. the head snapped from the stem, tore the crap out of the head before it ended up going through the piston perpendicularly and then just continually just chipping away at the dome on the head.