Plate 1 x 2 with Socket Joint-8 with Friction and Ball Joint-8 Lego compatible brick - PrintableBricks.com
Twin-socket for a Lego Ball-Joint (My Own Design - 4K) | Flickr
Bunte-Steine-Welt.de - Lego Plate 1 x 2, small Ball Socket on End (14418)
Amazon.com: Gobricks GDS-1205 Technical, Axle Connector 2 x 3 with Ball Joint Socket, Open Lower Axle Holes Compatible Lego 93571 All Major Brick Brand,Parts and Pieces (199 Dark Bluish Gray(072),10 PCS) :
LEGO® 6360827 67696 - ToyPro
LEGO Connector 2 x 3 with Ball Socket (89652) | Syd's Bricks
LEGO Technic Bricks - Modified 2 x 2 with Ball Socket and Axle Hole -