Well, the ones you mentioned: SCAR, M60, XM8
plus the INFMOD weapon pack that includes: AKM, FNFAL, HK416, M4A1, M14DMR, M16A4, M82A1, M93R, MAG7, MicroUzi, MP5A2, OICW, UDAR, and the Vintorez.
Those mentioned by Road are just property modifications of the existing stock and infmod weapons (ie. RIP-OFFS). The XM8 was the very first weapon mutator attempt and is of rather poor quality.