I would get under the car with a pick and hammer and have a really close look at all the seams holding the front clip to the underbody. I suspect if the control arm mount is shot, there will be other structural problems.
If it's just the mount area, you'd probably need to cut a good one off a donor car to make a decent repair.
a metro is a pretty simple car so if you have a mig welder then fixing it is pretty easy. The way the arm is mounted in there can be fixed without a lot of trouble if you are willing to take everything off the car around it. Pull the motor/trans and fender to see what you have to work with. Take the carpet out before you weld or the car will burn up, but the floor probably needs patched as well so it needs to come out anyway. I have a few extra metros here with no rust if you live near here it might be worth swinging by with it and getting some parts. I'm in WV btw.
I am going to have to do the same thing with my xfi real soon but I will probably just convert the car to a tube chassis and gut the unibody out of it.
If the alignment is still correct than welding it up should fix it - if it rips off like mine did then it is a lot more work getting it to align afterwards because the alignment adjustment is the bolts that screw into the bottom of the chassis and if they are solid rust then it can't be adjusted.