First of all, Spanish olives are well known in this country.
My personal favourites are 'Spanish' then 'Greek'.
As for which are the most sold, I am not sure. But the majority of 'Olive Oils' and 'Olive' product on our supermarket shelves are of Spanish origion. We do grow our own, but these are usually in the 'fresh deli' counters as well as the 'Greek' ones.
Olive oil features about 1/3 of our supermarket shelves (for that type of product) and is my preferred cooking oil. Usually cold pressed 'virgin' olive oil.
The main brand I can think of is "Bertoli" and they do oils, un-pipped olives in bottles (black and green) and non-stick spray. I have not seen any "Spanish own Brand" variety of these things.
As for the fresh Deli variety, most are either Greek or Australian. (And that includes the garlic and pepper, or chilli and wine etc etc varieties.)
The two premium and most used supermarkets are Woolworths and Coles. If you desire to find out which brands are sold, go to Woolworths 'home shop' join up and you can readily see the brands and items available for purchase from this store. (Although the amount of goods available from home shop is a lot less than is readily available in the real supermarket.)
I hope this helps you a little.