Amazon.com : Tiffen 77VND 77mm Variable Neutral Density Filter for Camera Lenses, Black : Camera Lens Round Filters : Electronics
Cokin 77mm NUANCES Variable ND Filter (5 to 10-Stop) CNV32-77
Ron Martinsen's Photography Blog: COMPARISON: Variable Neutral Density Filters (Singh-Ray, B+W, Hoya, Tiffen & Bower)
77mm Variable ND Filter
PolarPro 77mm QuartzLine ND8/PL 3 Stop Neutral Density and Circular Polarizer Filter
NiSi 77mm Circular ND Filter Kit | NiSi Optics USA
Bower 77mm Variable Neutral Density Filter FN77 B&H Photo Video
NiSi 77mm Circular ND Filter Kit | NiSi Optics USA
ZOMEI 52/58/67/72/77/82mm ND Filter Pro HD Multi Coated ND1000 Neutral Density Filter for Canon Nikon Sony Pentax Olympus Lens|density filter|neutral density filterfilter for canon - AliExpress
SLR Magic 77mm Variable Neutral Density 0.4 to 1.8 Filter (1.3 to 6 Stops)