He spawns in the very back of Nagafen's lair.
http://wiki.project1999.org/index.php/Zordak_Ragefire
At the end of the fire giants area, past Tranix, you'll come to the archway with the stone edifice in the shape of a dragon's head. Past that and up the stairs is Nagafen's lair where Magi Rokyl spawns.
In the very back of the lair against the wall inbetween the two large firepots, Ragefire spawns. He can spawn at any time when Nagafen is down, and his timer is 0-72 hours.
The spawn can sometimes be contested, so keep your friends close. If you actually camp the spawn, others will generally respect your camp, however, the letter of the P99 rules state that the first person to hand in the pearl wins. So, keep your friends close. A cleric and a well geared warrior can tank the human/spawned via turn in ragefire for a while as help logs in. If you can acquire a Donal's BP, you should be able to keep a well-geared 55+ tank up indefinitely.