Rare monster rates have recently been set to 1/500 instead of the long familiar 1/512 (With the exception of Kondy as his rate is different).
So, you will quickly realize that rare monster hunting is miserable and a trap that tons of players don't quite realize. Unless the item you are looking for specifically only comes from a rare monster, it's advised to hunt those items elsewhere. Trapping yourself into rare monster hunts due to the deceptive rates you see just isn't the move. People that do that within reason often have it set as a side task while focusing their primary attention on something else such as television, movies, etc.
If your attention is on the game, hunt it somewhere else if you can. Otherwise, I hope you find the item soon, lol.
(I'm also aware you recently dropped in from Ultima where you see rare monsters around every corner. This isn't the case here as they are meant to be rare monsters. So uh, yeah...They're rare :boreusip: