If you need to purchase Snow Leopard, you can still purchase a copy from Apple's online store's telesales agents.[1-800-MY-APPLE (1-800-692-7753) or Customer Service and Sales Support at 1-800-676-2775.] Ask for a Sales Representative.
Third-party sources for Snow Leopard are:
After you install Snow Leopard you will have to download and install the Mac OS X 10.6.8 Update Combo v1.1 to update Snow Leopard to 10.6.8 and give you access to the App Store.