You won't find them at home centers. You'd need to go to a drywall and steel stud specialty supplier...Just about any average city has one or two to service commercial construction needs.You say I can get load bearing metal studs. Okay, I'll look for those. Would they have those at a standard home-improvement center? Also, how would I support the structure while I remove the wooden studs? Do I have to use a jack or something? Or is that unnecessary?
Personally, I don't think that replacement of wall framing with steel studs is the way to go for most DIYers unless you have some very compentent assistance. To answer your "how do I support..." question, a temporary wall is normally built a couple feet away from the bearing wall to be removed/replaced, on either side of it. That wall will support the floor/roof above if done correctly.
I wish I could offer a solution other than the addition of refractory firebrick with refractory mortar to the wall, but I can't.