Hayoc can be found with NPCScan. You will need to add it, his NPCScan ID is 14234.
You can also use this macro to help find and tame him:
/cast Tame Beast
I'm not sure as to what his spawn timer is. I had to check the area several times before I found him. When he is up though, he is pretty obvious because of his bright skin. All of the other wind serpents in the area are green and blend in to the surroundings a lot more.
There are a total of five rare tamable hunter pets in Dustwallow Marsh. All of them are:
- Darkmist Widow, level 37 black & red spider
- Dart, level 37 orange raptor
- Hayoc, level 37 white wind serpent
- Oozeworm, level 38 yellow worm
- Ripscale, level 39 crocolisk