Any decent auto parts house will carry a large assortment of studs in different metals. I'd use Grade 8 stainless steel studs with bronze nuts, so they won't ever corrode together.

Another tip; get some high-temp Permatex silicone sealer, either the Bronze/Copper or the Blue (if the heat rating is high enough). A thin coat on each side of that exhaust manifold gasket will help seal it if it's warped in any way, and the next time you have to remove it, it should just drop off.

Replacing exhaust manifold gaskets is a real PITA so you want to avoid having to do it over, but if you do have to take it apart again, you can at least make the job easier by using the right materials now.

Now, another question...does your engine have small tubes running from the exhaust manifold to the smog system? Some type of exhaust gas recycling system? I bought a Chevy Caprice dirt cheap because it sounded like the top end of the engine was about to explode. All it needed was to have those little tubes replaced (about $25 in parts and 30 minutes work). The car ran perfectly quiet after that, and I sold it after putting about 50K miles on it. Got three times what I paid! :-)

What you're interpreting as a manifold leak might be coming from a sensor or something else screwed into the manifold. Sometimes you can feel the gas escaping by running your hand near the manifold, or else use a length of hose like a stethoscope to listen all around the manifold.