My SD/FM tank can go AFK in a +4 ITF surrounded by a full mob indefinitely. I don't think anything is unkillable in all situations, but this build feels pretty close.
Multi-Strike set does not exist
Can't get the whole set or individual pieces either one.
And in case you're having issues in getting this to work, put the Data folder into the same folder that your City of Heroes folder is in, not within the city of heroes folder. In my case it's in C:\Games