The amount of luxuries is dependent on the map size - not the actual size in tiles, but whether the map is small, standard, large, etc... The map size affects both the amount of unique luxuries and the amount of luxuries per type.
So what would probably work to get at least a few more luxes is go into CIV5Worlds (in Sid Meier's Civilization V/assets/Gameplay/GameInfo/XML), go to the huge world size and change all the data there - like size in tiles, amount of players on the map, etc, - to the map you actually like to play.
Then you'll still not get all. How to get all the luxes I don't know. It could be that Frontier maps type give you the best chances of getting the most luxes on one map, as the luxury distribution is different there; it also places random luxuries.