Adding a keyed lock to the outside of a RH Sliding door

Thank you for your patience in this matter. Your mortise latch looks like our 82-037. What you need to do is to determine whether this is the left or right hand door. This is determined by looking in from the outside. That said, look at our 82-316 and 82-317 key cylinders and see if these can work. If you need thumb turn as well look at our 82-043.

Great! Glad to hear it worked. Yes, this part is specifically for Andersen doors. You should contact an Andersen dealer if you want to make extra keys.