I just installed rear mudflaps ordered from Toyota dealer. They are for 2013 Yaris and with very little work fit great. Attached are photos of modifications I did , Part number, and finished work. I had to trim (with a pocket knife) a small area on back of the mudflap. It cannot be seen after installed. It did not require drilling holes into the body of car, I did drill 1 hole in the black inner fender liner. Image 2 shows mudflap before trimming and image 3 shows after trimmiing. Let me know how you like it.
If you look at the last photo you will see a chrome screw head. This screw goes into the fender liner. I did not drill into it I let the screw make it's own hole (same outcome). The car is really dirty, I had ridden it to work 3 or 4 days and did not want to get everything wet before installing the mudflaps. These mudflaps are pretty small for the price but I guess they will serve the purpose. I would have gotten back sooner but I had to go shopping with my son.
O'Reilly sells lots of mud flaps. Think I will see if they can get me a set for the Yaris. 73 bux is a bit much for me after all of my other upgrades. Will report what I find out, if anything. Dan