One of the floor challenges i have do to in the avatar sector is to kill a gold tricholoma which is easy enough, but they never seem to appear in the countless times I've tried. one time i killed 4 eliminators on the one floor and still no tricholoma. Am i supposed to do something to get it to appear or am i just unlucky?

No, they usually come to a sector at randome or when there is asystem sector challenge in defeating one.

If the challenge is to defeat one then it should appear on it's own.

First time I saw one was when in I fell in Agrabath in the cave of dreams,I failed to defeat it and when I went back to teleport I was murdered by the eliminator...

dont you worry i had the same thing happen to me but i only fought 3 eliminator and after that i gave up

^yeah i've given up too. It's like rigged or something.