Try the book; Art Flick's "new" Streamside Guide to naturals and their imitations
This revised edition of his earlier work was published in 1969.
Some of the Catskill style imitations shown don't see as much use as some more modern flies (but still work)
But full color pictures of the naturals and imitations are shown side by side

He recommends a Dun Variant as an isonychia dry
I would use a Slate Drake Comparadun, myself