All I can say is good luck. I have an Omega E3 with a cold light head. It came with one glass 5x7 holder. I have looked everywhere, including talking to Harry about two years ago. I did find half of one of the holders in a box of photo junk at my local flea market about a year ago. I am begining to believe that the world's supply of E series 5x7 neg holders were the cargo on board Amelia Earhart's plane.
Sharing your pain,