You don't need a Lion disc to install the bootcamp drivers (and even if such a disc existed it wouldn't have the drivers on as Snow Leopard did. The mechanism for getting the drivers has changed)
When you ran the bootcamp assistant to partition the drive for Windows you will have been given the option to download a driver set for your particular Mac. The driver set can be written to CD or to a USB stick and then, once booted in Windows it's used to install the required drivers.
If you didn't do this you can re-run the Bootcamp Assistant while in Lion, do the download to create the driver set and then cancel out prior to the partition part.
Incidentally, once you have the drivers installed, run the apple software update to ensure you have the latest version of Windows Bootcamp app, then go to the ATI website and download the latest mobility graphics card drivers for your particular Radeon card (you'll get better games performance than the standard drivers this way).