Paula,
we have been round this route recently. We could not find a 600mm built-in gas oven anywhere in Spain. Gas ovens are a rarity anywhere now and when you want LPG it's even harder. We got one over from the UK in the end. Make sure that you get one with a fan and a real thermostatic temperature control. As a tip... look on ebay for conversion jets, they are cheap and if you work backwards from the available LPG jets you might find an oven with standard jets for conversion at a decent price. It aint easy!  :-/