You do not have to use the original C\D. Use a different one, even borrow one and put in YOUR product key.
If you can not get a C\D with SP3. Borrow and earlier one i.e. SP1 or SP2. Copy a folder of windows to the desktop and slipstream SP3 into it.
Then burn the disk and use that.
Make sure you use only YOUR product key to activate it.