There are many companies that manufacture golf balls like Callaway, Taylormade, Bridgestone, NikeGolf and Titleist.
There are companies that make golf balls. However, they do not sell anything to make golf balls. If you meant golf ball marker, these can be found in local stores, such as Target, or online at Amazon.
There are many companies out there that make many different golf balls, but by the rules in golf it can not weigh more than 1.620 ounces.
Callaway make their own golf balls.
No, they haven't done so for 6 years or more. Golf balls today have soft covers and advanced cores which replaced the need for a balata golf ball, which just wasn't durable enough, which new balls today are.
The dimples make golf balls aerodynamic.
The Nike Corporation.
The makers of the Pro V1 golf balls claim that their golf balls are the '#1 ball in golf'. They claim that it delivers great distance, consistent flight, great green control and that they last longer.
You would design an experiment to test the balls.
There is no longer elastic bands in golf balls.
Custom golf balls can be made with the help of several design stores and websites. Golfballs, the "online leader in golf customization" is perhaps the best source for custom golf balls and is a great website to check first.