How do I reinstall the OS when buying a MacBook Pro since no install media was delivered to me?
There are plenty of ways around this dilemma:

Method 1: Upgrade to OS X Mountain Lion. You'll get loads of new features, and the all-new Recovery partition so you won't need discs. It should be free if your retailer was Apple Certified via the Apple Up-to-Date Program.

Method 2: Contact the reputable retailer. They should give you the original discs if you ask for them.

Method 3: Ask if you can borrow a friend's disc if you ever need it in the future.

Method 4: Contact Apple. I'm sure that if you describe your situation, they'll give you the SL discs at least.

Method 5: Purchase Snow Leopard. It's only $20, and it'll give you peace of mind if that's what you really want. You could buy it with the money you saved buying the refurbished Mac in the first place.

When you get your Mountain Lion/Snow Leopard installer, make sure you make a USB flash drive backup of it and keep it safe.

For Mountain Lion see here: Create a Bootable Mountain Lion USB Key Installer

For Snow Leopard see here: How to Create a Mac Snow Leopard USB Installer Disk