Although the above statement can be true in some cases, it is more likey you get a match with clowns and nems with natural symbiotic relationships between them in the wild.
Assuming you have true percs, the natural hosts are as you said above H. mag, and also H. Crispa, S. Gigantea, S. Mertensii.
The Mag is one of the most challenging species to keep alive of all hosting anemones, they don't ship well and are very unforgiving. They require strong lighting and very strong and intermittant flow.
The Crispa (sebae) I would say is the easiest of all 4 but very hard to find one thats not dyed or bleached.
I don't know too much about Gig's or Mertensii so maybe someone else can chime in...
HTH