We need to copy them and manufacture them ourselves with improvements, of course.
Yeah, um, we’ve been trying that and it hasn’t been going so well.
It’s kind of like US made AKs. It took the US fifty years to make an AK commercially that was as good as the Russian ones, and it still didn’t get decent until the Nodak Spud receiver showed the way. All the ones prior sucked and were unreliable. The problem turned out to be (in part) that American manufacturers were all trying to tighten up the tolerances and that resulted in AKs that don’t run.
The RD-181 is the version that the Russians are selling us:
https://en.wikipedia.org/wiki/RD-191
http://www.russianspaceweb.com/rd181.html
The AR1 is the best effort at an improved copy from US makers so far - looks better on paper but it hasn’t been working out well so far in reality.
https://en.wikipedia.org/wiki/AR1