You don't say what engine you have. But are you absolutely certain you aren't leaking oil from the valve cover and it's running down and looks like it's coming from the head gasket? I'm trying to think if there are any oil galleys through the block/head mating surface and I can't think of any.
You can't just throw any bolt in there. You need to go to a F/L/M dealer and buy a new head bolt. Using any other type of bolt is courting disaster.
Now, I hate to even mention this, but you may have a real ugly situation here. Take a piece of baling wire, or anything else you can use as a probe. Stick it down the head bolt hole and see how far it goes in before it bottoms out. Come back and let us know. Head bolts don't just fall out. I have never, ever seen one do that...and I've been working on vehicles since I was 14 years old...and I am one rusty, crusty ol' son of a gun! But they do break. You probably have a torque to yield fastener that gave up the ghost. I sure hope not though. Let's hope it just got left out for some dumb reason. Of course, maybe the block is stripped and the last person who worked on it just threw it together and sold it...
