Okay, I got em...

You have to clear the Ice Field completely first. Then, you just keep zoning until they appear. They will only appear one batch of five at a time. To get them to respawn, I went north from the Ice Field two screens to the little boss area, then came back. It will respawn the desired mandragoras and not the standard enemies. Needless to say, you have to do this 14 times so it takes quite some time.

My next target are the Ghosts in Gamarsythe Waterway. I cant seem to find them at all. Anyone know where they appear?

I think I only need 4 or 5 more normal creatures, 3 rare monsters, Yiazmat and Omega... then I am finished