As far as I am aware, there is no such feature in ATLAS or Athena. What is your use-case for a drug strength table search?
It is something I have been looking for as well while working on a mapping of a national drug register to RxNorm. I ended up just creating sql queries myself (which was quite straight forward).
Maybe we can make a combined effort to implement this functionality (following the open-source motto: if it is not there, make a contribution).