By Odin.Llewelyn 2012-01-10 07:36:40
Unfortunately from my experiences these mobs do seem to be in short supply.
On the bottom floor (Orc/Quadav) you can switch between the Hydras around the tower at H10 and the ones surrounding the pond at G10. There's a SMN and DRG at the pond along with another DRG that shares a spawn with a NIN or SAM at the front of the pond (near the ???). At the tower there is a BST and *possibly* a DRG, though I don't remember too well. I'm thinking no.
On the Yagudo floor go south past the TE statue and you'll come across some hydras you most likely have already seen before. There is a SMN around the middle of the hydras and a BST all the way on the far SW end of the bunch. There may be another SMN or DRG lurking around this area but in all honestly I've never paid attention to SMN DRG and BST hydras.
I've never checked the Hydra on the Goblin floor but on the Yagudo and Quadav/Orc floors that's the best you'll be able to do. Hope this helps~