Silverline 5700 Series Lock tab
A quick learner from Warwick, RI says:
March 31, 2016
I just bought my house and the slider was there with a door handle and lock function but no female part. I took a picture of the missing piece from someone else's door just like mine.
Paul from SWISCO responded:
April 4, 2016
Silverline no longer provides this exact keeper. For their Series 5700 door, they recommend the 89-029 white keeper. Even though it looks different than your neighbor's, I think it should still work. You just may have to redrill your installation holes.