l have a 2000 Mercury Grand Marquis GS. If it did come stock with one, where can l get one at? How hard is it to program?

Yes it did come stock with a keyless remote. You can buy the keyfob on ebay for something like 10 dollars. l have no idea on how to program it though. Sorry.

Yes you can buy one on ebay and l believe the program instructions are in your owners manual.

The keyless remote came standard on all 2000 Mercury Grand Marquis GS that had the Convenience Package on it. The easiest way to tell if yours has the Convenience Package is to see if it has the keyless entry remote keypad on the door. If it does, Your Grand Marquis came standard with a remote.
You can get a remote either from E-BAY by paying $10.00 - $15.00 or by stopping by ur local FORD Lincoln mercury dealership. They all have extra keyless remotes from trade in vehicles. They will usually give u one for nothing.
You program it by:
1) Putting the key in the ignition.
2) Turning the key to the on position( without turning it on)
3) Quickly turn the key to the off position
4) Repeat until u see the doors lock, then unlock.
5) push any button on the keyless remote.
6) Wait for 2 Minutes before u turn the key, push any buttons or try to get out of the car.

Hope this helped you!