If you are looking for an RNAV rating on the Garmin 530 or 430 take a look at RidgeAir in Blenheim
They have a great Seneca IV fully equipped with KFC 150 Autopliot Flight Director and coupled Garmin 530 the aircraft is also fully deiced with radar
Their instructor RM is ex GA and Airline and they only cater one on one, so you get some great tuition from someone who knows how it should be done with real experience.
If you'd read earlier posts you'd know that the OP wasn't asking about a GPS but the Garmin G500 which is an EFIS.