This is a question about shelf pins, in this case 5mm plastic shelf
pins. I cannot find a source for the particular shelf pins I need.
Most shelf pins that are available have a, well, pin, of either 5mm or
1/4" that inserts into a hole in the vertical rail. The ones I need
have an added twist. The pin is shallow and has wings on either side
such that the pin is inserted with the wings pointing up and down and
then twisted a quarter turn to lock into place.

I have visited numerous hardware stores, Home Depot, and gone online
trying to find these shelf pins with negative results. Maybe they are
european or scandinavian, I don't know. Does anyone recognize these
pins and know where I can buy them.Again, they are plastic, 5mm, shelf
pins that twist a quarter turn to lock in place.

Did you ever find a supplier for the shelf pins you asked about? I am
looking for the same thing and have done the same as you. no luck at
the home improvement centers or online. I have taken to emailing other
hadware suppliers to see if they know about these. Please let me know
if you have found anything and I will do the same.

Lowe's Building Supply carries a variety of shelf pins in the
specialty hardware area binned in drawers.  Also you can get them from
www.widgetco.com