http://www.eqemulator.org/forums/showthread.php?t=21138
Here is information I have found in the past related to spawning Quillmane, but I've never found actual information regarded to drop rates. I'm not sure that our server uses this code either, though finding it on the EQEmu page doesn't hurt the case. Furthermore, I've always wondered how people label drop percentage rates on the wiki for any mob?
From my anecdotal experience, it seems like the lioness tends to pop Quillmane more often; if I have someone kill elephant calfs while I kill lionesses, she usually tends to pop after I've killed 8 lionesses while calfs have been constantly killed. Furthermore, the median number of Quillmanes just to get a cloak from my personal memory is 5 to 6. From my personal experience, killing Quillmane 10 or more times to get a cloak appears to be an outlier.
Obviously, everything depends on random number generators, but I was wondering if anyone had ever seen the source code (similar to the link I posted). I could try to run some data analysis, but my last statistics course was a few years ago heh.