they are mostly univeresal, but pretty universaly shitty as well.
Removable, I think these are pretty ok http://www.bhphotovideo.com/c/product/839296-REG/Lens_Gear_605859_LENSGEAR_UNIVERSAL_LENS.html
Othervise, find a cnc shop in your area and have them made them, out of delrin if I remember corectly and just leave on the lens. I think there was a guy on ebay selling cncn made ones, custom as well.