When I lived in Australia near Byron Bay, there was a lot of good citrus available most of the year. It has been quite a few years now, so I do not remember all the details, but there where mandarins, navels, tangerines, blood oranges, all sorts, at reasonable prices, not all certified organic, but quite a few where. I do not remember the season exactly, but think it is pretty much year round, and quite local, though there is definitely a bit of a peak and shoulder season, maybe someone else can fill you in on more specifics, or you could try googling a bit more to get a better idea. There is also a lot of pineapple, banana, custard apple, etc. that grows in or near that region.
I'd choose oranges from south of Italy, more precisely from Sicily!
Most of oranges in Italy are grown in Sicily although there are three different types that spike out from all others:
-Tarocco (my favorite)
All these have been marked IGP (Protected Geographic Location, in Italian would be Indicazione Geografica Protetta) by the State of Italy which means they can only be cultivated in certain areas of the island.
There oranges have 40% more vitamin C than other types and you won't believe how sweet they taste! When in season I have a liter and half for breakfast every day!
You must try them once if this is your most enjoyable fruit ;)
I grew up eating fresh picked citrus all year long, many types all year long when I lived in Southern California, the valenci oranges on this one propert I rent on in he hills along a perrennial stream had the best ,there was always flowers/fruit set, medium green fruit, "ripe oranges", and then also on the same branch there is shrinked up golden oranges that have some greenish moss algae and scales on the top half of the fruit and they get leathery skin like a firm Hakey sac . When I touch them they fall into my had or they are found on the ground in the soft mulchy soil along side a perennial stream, anyways now I live on the big Island Hawaii and i eat citrus all year fresh picked all I can eat proly eat 30 types of citrus thruout the years hhhhhre most of the fruit trees I eat from the fruit rots on the ground and the wild life use it .
Many types of old seedling maderians are all over the Hawaiian Islands , 100 year old citrus trees all over