Actually, this mob doesn't have a longer respawntime than the rest, it's just perceived as such because he spawns in the hive and then wanders down to the east farm where he then stays. If you want to kill it slightly faster, you can wait for him in the large open area between east and west farm - set up your camp along the southern wall and he'll path right into ya while nothing else comes close. (of course you'll have to kill him once at the east farm first since he doesn't path back up)
Drop rate is abysmal though. Killed somewhat between 20-30 and nothing yet.
*Edit* We finally decided to go into the hive and got 2 drops in 38 kills. With a good group (speaking skill-wise) you can get there without much problems. Should you go there, a good spot to camp would be the room with the fake floor. Head left once you get to the spiral-ramp and into the first room there - drop through the fake-floor and you'll only have 1 mob in the room. (a cliknar eucryptoid btw.)
Agree! the room below the fake floor is best camp for this drop. Killed the eucryptoid in the room and the 3 out on the spiral ramp... boom 2 drops and gate on to LC.