... Can I find such a driver somewhere?
Have you checked with its manufacturer?
If you want to upgrade OS X the easiest and least expensive option would be to purchase Snow Leopard from Apple. The intervening OS X release, Leopard, is no longer available from Apple and is unreasonably expensive from aftermarket sources.
To purchase Snow Leopard online:
Elsewhere: call the phone number in the Apple Online Store
Apple's price is $19.99 or £14.00. It is not available to download from any legitimate source.
Mac OS X 10.6 "Snow Leopard" System Requirements
- An Intel processor
- An internal or external DVD drive, or DVD or CD Sharing
- At least 1 GB of memory (RAM) (additional RAM is recommended)
- A built-in display or a display connected to an Apple-supplied video card supported by your computer
- At least 5 GB of disk space available, or 7 GB of disk space if you install the developer tools
After you install Snow Leopard you can decide if you want to upgrade OS X to the latest version, Mountain Lion. Mountain Lion is available in the Mac App Store, which is available to you after upgrading to Snow Leopard.