https://annas-archive.org/md5/e912dea2423647376d23c54653f9586b (digital)
https://www.zvab.com/servlet/SearchResults?isbn=9789985037058&cm_sp=mbc-_-9789985037058-_-all
https://www.abebooks.com/servlet/BookDetailsPL?bi=31539773289&cm_sp=det-_-bsk-_-bdp
None of these are in English
How do these two compare in terms of rigor? Biochemliteracy seemed a bit "fluffy" to me at first glance (middle school level rather than high school level). Is this true in your experience?
https://www.bluebonnetscholars.org/course/accelerated-studied-in-physics-and-chemistry/
Look at Memoria academic, Kolbe Academy, and Wilson Hill Academy
My guess is that Master's degrees at US universities have a known standard of rigor and provide research opportunities to their students, while most international undergrad programs do not have either.
https://www.complexityexplorer.org/courses
They have a bunch of free courses (cohort-based and self paced) on very interesting topics - think fractals, complex system, chaos, etc.
Will Physics 1 and 2 involve practicing calc 3, linear algebra, or diff eq? Does you university have an honors calculus section that would give him exposure to proofs without being as involved as the proof writing course?