Sure, and I admit I have no idea how much lead building such a spaceship might take, but keep in mind 2 things:

1) "More than half of the lead currently used comes from recycling." (from your article) - Once the spaceship is built and has left Earth, the lead is essentially gone (for the time being), so the more of those we build, the fewer lead we will have to recycle, and it will get even more difficult to build additional ones.

2) 400 tons for a small capsule, and consider they're proposing a spaceship in which multiple people could live in autonomously, i.e. they need places to live in, but also room to grow food, process their waste, etc. So I'd guess it's much higher than you seem to have assumed.

Oh and btw, I'm fairly certain we also need much of that lead on earth - hence why we're producing so much of it in the first place, so it's not like we have some spare lead in the order of magnitude of, say, 10000s (I'm really just guessing here, though) of tons lying around collecting dust.

For 1) That's going to be true of any resource that's used in spaceship construction. If you're building interstellar ships at such a scale that you might conceivably run out of stuff to build them out of, it's a fair assumption that you have the capability to go and mine the rest of the rocky planets in the solar system.

2) That 400 tons is not going to scale up with volume. Density of lead is around 650 lbs/ft3. Let's say you have a big ship, a mile in diameter. And let's be generous and put a 4 ft shell of lead around the whole thing. 4/3pi(5280^2-5286^2) * 650 * 1/2000 = 57000 tons of lead = 52000 metric tons. A drop in the bucket, tiny compared to the amount of steel and other material that would make up the rest of the structure. (Annual steel production is around 100 times more than of lead. We won't be running out of it either.)

The bottom line is that unless you're talking about transuranics or other extremely rare elements, or are building things at comically large scales (ie: thousands of ships) amount of construction material is not going to be a limiting factor in starship design.

I assume that we'll somehow solve this one with a 'force' field of some sort in the future. Think about it. The Earth isn't surrounded by lead, but we are still protected from the radiation. I imagine that if we can harness a black hole for propulsion we can somehow use it for power too??? Then we just use some of the power to create a magnetic field that blocks/reflects/deflects the radiation.

> The Earth isn't surrounded by lead, but we are still protected from the radiation.

A thick atmosphere accomplishes roughly the same effect as a few feet of lead. A magnetic field could deflect incoming charged particles, but I'm not sure if a "shield" is feasible, due to any side effects that such a magnet might have.

I was under the impression that the Earth's magnetic field was doing the majority of the work. IIRC, the reason that Mars has no atmosphere is probably due to lack of a (or just a weakened) magnetic field, causing solar winds to strip away the atmosphere.