deerjackie,
I haven't seen one marketed specifically for a Knight, but the older Knight's used Timney triggers so I am sure there will be one that fits. Timney has several triggers so be sure before you order.
If you have one of the newer Knights such as Revolution/II, Vision, KRB7, KP1, you will have to figure out the radius and width because I am sure there are slight differences.
Check these ones out, should be able to find one that fits like a "shoe".
Scroll down, it shows how you can find the correct curve with U.S. coins, then it is a matter of measuring the width.
Example trigger shoe.
http://www.t-grips.com/TriggerShoeHomepage1.html