I have an Identi-View visual solar filter for sale. It has an inside diameter of 4 3/8 inches, and has shims to fit dewshields up to 1/2 inch smaller, I think. I used on my Stellarvue AT-1010 and it fit perfectly. I think it will also fit the ETX-90. it is in like new condition with the box and all paperwork, I used it twice (I sold the scope.)
$65 shipped to you.
Thanks for looking, Eric