As you've observed, the rules as written offer no way to acquire an Apallie familiar. However, by comparison to the other entries on the Improved Familiar list, a generous GM may let you adopt an Apallie familiar with the Improved Familiar feat and a 7th level restriction. It has no particular abilities which are unbalanced for a party to have access to at that kind of level, and the CR2 creatures on the improved familiar list mostly have 7th level restrictions.
Based on the description of the creature, though, it may not enjoy being a familiar very much. A pathological belief that it is a genuine civilised humanoid seems built-in, which would preclude being some wizard's familiar. Also, if the adventuring party does as adventurers do and goes for long walks in the woods, through ancient ruins, and other places far from civilisation, that'd conflict strongly with the Apallie's desire to hang out in society.