Depending on your local laws, and what sporting good stores you have near by...Walmart, Kmart, Dick's sporting goods, someplace that sells hunting supplies, the problem is in a large city there may be ordinances against slingshots of one type or another that might make them hard to find I would say your best bet would be to order on line.
Welcome. Most sporting goods stores carry slingshots and steel ammo. If you have ever done ebay you can find many types of slingshots there. Also many of the members here on this site make and sell great slingshots. If you browse here you will see---- Flatband, Bunnybuster, A+ slingshots ,Dankung, and Smitty and many others just to name a few. You can't go wrong, these guys are serious craftmen with a great and durable product. I own a few they made and the quality is awesome. hope this helps