Very similar to Marty Robbins' ballads are "Matamoros", "El Diablo", "Cross The Brazos At Waco" all by Billy Walker
"Belle Star" by Jim Glaser appears on the Johnny Bond album "That Wild, Wicked, But Wonderful West", and wrongly credited to Johnny Bond. Jim Glaser sang on many of Marty Robbins' western ballads, and recorded this and several other songs as a solo artist. "Belle Star" is the only one I can locate, but there was an album out in the mid 1960s.
Other noted singers of western ballads are:
Gene Autry, Johnny Bond, Rex Allen, Chris Le Doux, Roy Rogers, Johnny Western, Rex Allen Junior, and Tom Russell (great writer!).
Johnny Cash ("...Sings Ballads Of The True West") has done a few, too, as have Bob Dylan ("Pat Garrett & Billy The Kid"), and Willie Nelson ("Redheaded Stranger").
Very interesting is the concept album "The Legend Of Jesse James" featuring Charlie Daniels, Levon Helm, Johnny Cash and Emmylou Harris.