AHi There! Any suggestions on how to make or what to use for the "needles" ion fondant cactuses? Maybe white jimmies? I'm stumped! Thanks!!!

That would work.   You can also use gumpaste to make them.  I did sesame seeds with gumpaste for a hamburger.  It was a bit time consuming but they dried hard.  Once you make the needles and they get dry you can insert them in the cactus.

AThank you for your suggestion. I also heard that I could use royal icing. This will probably be faster and less time consuming, hopefully! :)

I am not a royal icing user so that never comes into mind.  But definitely that would work and less time consuming.

You gave me now a good idea for future use.