Maybe.
Note that these kinds of composites are exceedingly common these days.
Like "I can buy it online from amazon.com" common for some and "random online metals shop" for others.
Now certainly, not what Apple's gonna do, but more in the point of "there's a very very large set of companies with large amounts of expertise in this". I have pretty strong doubts you'd go to mclaren for it.
Apple's cases are nice, but "the best work in the world with [aluminum]" is a real stretch. They're not complicated or high precision, they're computer cases.
There are people making turbines with aluminum, and medical equipment, and machine parts that are accurate to an order of magnitude more than Apple's pretty phone case.
You can buy a lot of materials, but knowing how to manufacturer with them is a different skill. BMW has more experience with carbon in automobiles, but that's a whole other level of acquisition.
McLaren built an entire car out of carbon fiber. Good luck figuring that out from your Amazon purchases.
Material availability isn't really the issue, although supply is still very constrained due to the dominance of the aerospace industry.
The real issue is expertise. High performance composite manufacturing techniques are jealously-guarded trade secrets. The amount of information in the public domain is really very limited.
Like "I can buy it online from amazon.com" common for some and "random online metals shop" for others.
Now certainly, not what Apple's gonna do, but more in the point of "there's a very very large set of companies with large amounts of expertise in this". I have pretty strong doubts you'd go to mclaren for it.