lardog18:
If nothing else you should be able to purchase the same type of golf ball your where using.
You can purchase balls in round, but it has to be before you run out.
A good habit to get into is as soon as you start your round click on your name, check 'equipment'. This will tell you how many balls you have left. If you are low you can go to your other window and buy more balls and they will show up in your bag.
As I understand it the reason that you cannot chose a different type of ball has to do with the rules of golf. You cannot change ball types during a round. The compromise, instead of having you forfeit the round, they give you the starter balls.
Happy hitting.