Aussie country music icon Adam Brand. The Muster announced today that 12-time Country Music Award winner Brand, along with Cold Chisel legend Don Walker, iconic rocker Diesel, Shane Nicholson, Casey Barnes and Gympie’s own Caitlyn Shadbolt among the additions to the 2021 Muster line-up. 2021 Muster headliner Don Walker, pictured with Paul Kelly. Picture: Supplied by Rina Ferris. Lee Kernaghan, Kasey Chambers, Beccy Cole and Troy Cassar-Daley had previously been announced as Muster headliners last December. “Even if you hated country music you would love the Gympie Muster, and I reckon it would turn you,” Brand said in a statement. Australian rock legend Diesel.