You can get any spheres worth getting at the monster arena. The specie creations will drop teh attribute spheres like Str+4, Agl+4, Mag+4, Acc+4, etc. The fortune and luck+4 spheres are gotten from the second original creation, and luck spheres come from the first original creation, earth eater.

You have to capture the proper number of monsters to unlock the beasts though. If you aim straight for clear spheres (5 of each monster in spira.) you should probably unlock all of them you need for the time.