Heliopan ships Vario ND variable filters in sizes from 55 to 82mm: Digital Photography Review
Neutral Density 3.0 Filter - Neutral Density 3.0 Filter - 55mm Neutral Density 10x (3.0) Camera Lens Filter - Heliopan US
Neutral Density Variable Gray Filter - Neutral Density Variable Gray Filter - 62mm Variable Gray Neutral Density Camera Lens Filter - Heliopan US
Amazon.com : Heliopan 52mm Neutral Density 8x (0.9) Filter (705237) with specialty Schott glass in floating brass ring : Camera Lens Neutral Density Filters : Electronics
Heliopan 30.5mm ND 1.5 Filter (5-Stop) SPECIAL ORDER – A&S Camera & Pro Video