You could mine it from asteroids, which have plenty of base metals. There's already a speculative market for investors wishing to mine them. The only thing is; the technology for transporting it around doesn't exist yet. (We can land probes on them however for recon, but that's about it so far!).
Why do people keep insisting on the Dyson concept as though it was real, even though it's just the fanciest thing we can imagine with our current understanding of physics?
The same way in the 19th century nuclear power couldn't be envisioned, there's definitiely a bunch of technology we don't know about now that an alien civilization could be using; we could even be observing this right now and we would be none the wiser. Talking about Dyson shperes, or swarms, or rings, and then concluding that there's now alien civilzations because we can't see them is just anthropocentrism, failing to consider other possiblities
On Earth, none of those are available in the quantities needed to provide sufficient energy for us (close to a planetary civilisation in energy needs) on the scale of millions of years.
If you want your civilisation to not deplete available energy in the next million or so years and to allow for growth of energy demands in that time, you're going to have to make use of star power.
A planet only gets so much starlight that it becomes a limiting factor in energy budget. The easiest next step is to make more use of the abundant energy source next door: your star.
There are other options, e.g. using black holes. But those are orders of magnitude more challenging: black holes are extreme stars (extremely far from any developing civilisation).
On Earth, we've seen that every leap-frog in civilisation (fire, agriculture, industrialisation, ...) increased the available energy budget by orders of magnitude. There's not that many orders of magnitude left on this planet to grow further; if we want more, we'll need to get it from elsewhere.
Alien civilisations that remain bounds to their planet's energy budget similarly must remain stuck at a certain level of energy use. They can make advances in efficiency, but their total energy budget is capped.
When in the past, unanswered, mystery questions like these were finally answered (for example "how come light seems to appear in discrete packets?"), the answer ended up being a door to a completely new understanding of reality, and not a little footnote question at the End of Physics
So yeah, when there are no more unanswered physics questions, I will consider that the laws of physics have been exhausted. Right now that's not the case.
Seems like it would require, at minimum, several planets worth of raw material.