HL and Inferno missiles..

Is there any certain time or DLC or mod that I need to find these.. I found one mech with the Hot Loaded missiles once in the past yr I've been playing it.. Inferno missiles I haven't seen or found yet.. I have up to Solaris Showdown. Don't have Shadows of Kerensky or any of the Clan games.. I'm 54 and play by myself on the PC so don't know if I'll get the Clan ones or not seeing how those Elementals are tough to kill in group play.