Well, I recently went through my boxed archives of Beatle collectibles and I have the Club Sandwich/#4/AugSept, 1977 you are looking for. I am really lookiing to sell the entire set and I'd hate to break it up. I have the following Club Sandwich issues: #3 thru #27 (no #28, but it's probably somewhere) #29 and #30. All are in great original condition except for #25 that has a bit of water stain on the cover.
I also have songbooks "Songs by McCartney" 1970, "Wings Wildlife" 1971, "Ram" 1971, "New Songs of Paul McCartney" 1974, "Wings at the Speed of Sound" 1976, and "Venus and Mars" 1975. Plus, lots of promotional posters, postcards and a cool desk calendar in prime condition -"Matey for '80" featuring Paul's son James on the cover and Linda's photography.
There's other stuff too like magazines featuring the macca's on the cover such as Life Magazine, April 16, 1971, Us Magazine Mar 21, 1978 both in great condition/sleeved and many, many more too long to list at the moment.
Let me know if you're interested.