What are some good places to buy surfboard racks?

As you did not mention where you are located, I would suggest the World's No1 Surf and Sports Storage Systems provided Solid Racks - https://www.solidracks.com/.
Also SurfStitch are a great supplier http://www.surfstitch.com/category/surf/surfboard-racks Pat Hawkins

http://www.surfstitch.com/category/surf/surfboard-racks http://www.esurfboardracks.com/?gclid=COaR9-TYk7gCFZBj7Aod4TkAOw