Well sure. But if Russia has initiated effectively a war against an allied nation, and we see the missiles Russia shoot into Ukraine contains these commodity chips... we need to have a discussion with customs.
We can see that Russia prefers to import these $1 or cheaper chips, rather than build their own.
It's not possible to stop them. These chips are literally commodities - some of them are actually technically counterfeit and you might never notice. The Russians will buy them from second hand markets, just like everyone else. They're just too cheap and too common for sanctions to be enforceable.
The point isn't to make things perfectly tight. Its to make Russia work harder to penetrate our defenses and increase the costs for them.
Every black market trick they do to penetrate customs to get these chips is another trick we can track and close down. Its ongoing work, but likely important for other wars that have yet to come (see China, who might pull the same crap if they start anything with Taiwan).
It's not a question of customs. These chips are commodities and they can be bought by the thousands from, say, China - they aren't generally made or finished in the US either. US customs don't have a say in this.
We can see that Russia prefers to import these $1 or cheaper chips, rather than build their own.