Posted 30 May 2017 - 07:03 PM
Just in case you were wondering, the most current macOS version Mac can likely run (I am 98% sure I have the right model from your description) is 10.7.5 (aka Lion), which is two versions newer than Leopard (aka 10.5.x). You can certainly find Snow Leopard (aka 10.6.x) retail discs* on sites like eBay and likely even find a Lion install disc (I found one). Lion is a bit trickier as it was primarily available through the App Store and all App Store purchases are tied to an AppleID, so you would need the AppleID used to purchase Lion through the App Store in order to install it if bought through the App Store. Apple did, however, also sell install USB drives and I believe even optical discs for it that were not tied to an AppleID. So, you just need to be careful about which you buy if you choose to go that route.
* For install discs that existed prior to Apple moving all OS upgrades/purchase through the App Store, there are two types of install discs. There are retail install discs. They will have a colorful label on the disc. Retail discs can be used with any Mac that supports the version of the macOS. Then there are the recovery discs that originally came with a Mac. They will have a mono color (typically grey) label on the disc. Recovery discs will ONLY work with the specific model that they originally shipped with. In other words, if you Mac is a 2006 original 15" MBP, then a recovery disc from a newer MBP or from an iMac will not work with it.