I used a shaker can of "cast iron" paint. Spray some into a small plastic cup (like the cap off the can) and use a small brush to apply the paint. The Cast iron paint is a high temp paint, and I used it on the master cylinder as well as the exhaust manifolds. I am impressed at how well it stands up. I can dig up the can if you want the brand name.

As for the alternator, I haven't tried anything on that. Mine's chromed (from the previous owner). I think painting would be OK, but I would make sure no paint got inside - there are vents on it housing. A brush would be a safer way to go rather than the shaker can.

I'm pretty sure the paint I used was from Crappy Tire - VHT brand if I remember correctly. I'm impressed with it. Just wire brush the loose rust off and about 4 years later it still looked pretty good. Touched the exhaust manifolds up again this summer. The master cylinder still looks great. Brake fluid destroys paint, so be careful adding fluid.

Good luck with the alternator.

I'm a little late however Eastwood has a line of paint for these applications.

Click Here for Eastwood Underhood Paint Line 

This is what I used on the manifolds and master cylinder, and yes, got them at Canadian Tire. I don't know if they still carry it, but I hope so. My can is probably 6 years old and still at least half full.

I am sure the Eastwood stuff is great too. Wouldn't it be nice if they had a better distribution system in Canada?

I see they have lower temp (500 F) cast iron and cast aluminum paint from Duplicolor. I haven't tried those. Likely fine on the brake cylinder, but I wouldn't trust it on the exhaust manifolds.