NEC 2016 AFCI question
GE (THQL) AFCIs don't come in two pole any longer -- because they don't need to

Your apparent lack of ability to find two pole THQL AFCIs is actually due to a manufacturing revision to the single pole units.  Mod 3 single pole THQL AFCI breakers can be handle-tied for multiple pole applications, as they do not use a CT-based trip for arc-to-ground detection.  (You still need to wire the load neutral to one of the AFCIs, but either one will do -- you don't need to connect it to both.)

See this GE handout for details.