need help finding a part

i hope this is the right place to post this lol i rarely venture out of moto related. i have an 05 yz 125 with an athena 144 kit & during a race i noticed my bike was not feeling right so i pulled off to check it out. the very first thing i saw was antifreeze leaking from somewhere & after looking at it a bit more i found that my cylinder head has a crack in it. has this happened to anybody else? can i just buy a new cylinder head without having to buy a whole kit? should i email athena, or would i have better luck finding the part online? any help is appreciated.