Alpo let you off way too easy with such a good answer so quickly
ida used the missing part as a start to the holy grail--
seek & ye shall find:
....the junk/parts draw in the kitchen
....those draws & small cartons in the garage
....and lastly: the basement--where you will find stuff you totally forgot you ever had, let alone lost.
than again, you will of course find it anyways within a couple of days after the replacement part arrives from Ruger.
back of a draw-----
have you taken all the draws out and looked inside what was left?
and a base pin is perfect size to roll into the slot of the back of the draw that the bottom 'should' be slid into.