Manfrotto 577 Quick Release Adapter with 501PL - photo/video - by owner - electronics sale - craigslist
Manfrotto 357PLV-1 Sliding Plate with 1/4"-20 & 3/8"-16 357PLV-1
CAMVATE Manfrotto Camera Quick Release Plate Mount 1/4" 3/8 for 577/501/ 504/701 | eBay
CAMVATE Slide-In QR Adapter Baseplate for Manfrotto 577/ C2406
Amazon.com : Manfrotto 577 Rapid Connect Adapter with Sliding Mounting Plate for Bogen/Manfrotto Tripods : Manfrotto Quick Release : Electronics
Amazon.com : Neewer Rapid Connect Quick Release Sliding Plate Camera Mount with 1/4" and 3/8" Mounting Screws for Manfrotto 501HDV 503HDV MH055M0-Q5 : Electronics