Pturn
I think most of the spraying is done by air tractors piston and turboprop, piper braves and the odd ag-cat and PZL.
Avialsa would be a good start followed by Martinez Ridao and the companys at Cordoba. FAASA only have a couple of ag-cats left.
I don't know much about worldwide spraying operations but there seems to be a number of accidents in Spain each season, from the aircraft I have seen some looked a bit nasty.
Out in the countryside most Spaniards don't speak a second language so learning Spanish would be highly recomended.
Good luck.