Some of this may be helpful to others that own Tektronix 'scopes.
I wanted to replace the smoked filter on my 7603, but could not find one for a reasonable cost.
Lowes has a small piece of 0.080 transparent plastic for less than 4 dollars. I bought a piece and cut it with a jig saw to match the size of the
smoked filter. I then glued a piece of GamColor theater gel to the back side of the plastic to make the filter. It seems to work well. It isn't the
same as the one from Tektronix, but it is the same color and was inexpensive.
So...plastic piece $ 3.78
GamColor #790, $9.95 ( 20 x 30 sheet )
Hope this helps someone.