Dimpled Golf balls because they fly farther than smooth ones. (I don't even know where to buy smooth ones). :P
Yes, they do sell floating golf balls. If you want to buy for your own, you can buy it from eBay online store. It ranges from $2.00-$5.00 depending on the color , the kind you want to have.
There are many good examples of new models of golf balls available to buy. For example, one can easily find that Titleist golf balls and Nike golf balls have new models of golf balls for sale.
One can buy novelty golf balls at sites such as Golf Balls, Sports Gifts, Global Golf, and Golf'un. One can also purchase them online from Amazon and eBay.
Cheap golf balls are generally very hard, which means that it is difficult to control where they go. It is never okay to use cheap golf balls and one should just buy the high-end ones.
One can buy monogrammed golf balls at any sporting specialty stores such as Dick's Sporting Goods. Other miscellaneous websites are GolfBalls, Monogrammed-Golf-Balls, and Golfsmith.
One might purchase Srixon golf balls from Amazon where one can buy a dozen of them for $19.90. One can also buy them from Drummond Golf, Global Golf and eBay.
Walmart
Yes, you can buy them online and in sport shops.
The best place to buy vintage golf balls is Ebay. They have just about every vintage golf item you could imagine. It is probably the place where you will find the best deals too.
No golf balls do not melt in water that way.
Green staked tree, Ground Under Repair, casual water, water in a bunker, animal burrow, cart path (check local rules though), embedded ball in the fairway, tyre print (from tractor or heavy vehicle).
Then you go out and buy more.