Can anyone recommend any Spaghs that have friendship as a major theme? The ones that come to mind that have this theme are Ace High (friendship and betrayal), Ben and Charlie and I would also say Dead Men Don’t Count (brothers who are best friends).
So, any other films like these?
While it is not exactly a great movie and I can’t say exactly why, the first one that pops into my head is Deaf Smith & Johnny Ears (1973) with Anthony Quinn and Franco Nero.
I’ve actually been thinking of watching that one because Franco Nero :3
Maybe Life is Tough, Eh Providence? silly but pretty funny.
Tomas Milian and the big guy have a central friendship, if I remember right.
The Forgotten Pistolero has themes about friends and family (its also based on Orestes). Vengeance and 5 Giants from Texas involve the main characters avenging the death of their friend. Massacre Time and Vengeance is Mine are more about brothers than friends but the theme still applies. The Unholy Four is about four friends who escape an asylum and end up helping the main character who has amnesia. Woody Strode and Peter Martell share a close friendship in that movie.
I dont know if Today We Kill Tomorrow We Die counts since the plot involves the main character getting a team together to kill the villain but it ends up with the group becoming friends.
Those are some very good examples. You referenced The Forgotten Pistolero so great first post! 
Welcome to the web site!
The Unholy Four there’s a strong bond between the Peter Martell and Woody Strode. The Spikes Gang, also The Moment to Kill with Walter Barnes and George Hilton.
I believe—according to Wikipedia, at least—Leone said that Duck, You Sucker was mostly about friendship.
Not sure if it’s spoilers, but here’s his exact quote.
I chose to oppose an intellectual, who has experienced a revolution in Ireland, with a naïve Mexican… you have two men: one naïve and one intellectual (self-centred as intellectuals too often are in the face of the naïve). From there, the film becomes the story of Pygmalion reversed. The simple one teaches the intellectual a lesson. Nature gains an upper hand and finally the intellectual throws away his book of Bakunin’s writings. You suspect damn well that this gesture is a symbolic reference to everything my generation has been told in the way of promises. We have waited, but we still are waiting! I have the film say, in effect “Revolution means confusion”.