I just asked the same question somewhere else. Candlekeep publish a PDF magazine called Candlekeep Compendium, so they might be able to help organise this.
The section 15 entries of Bestiary of the Realms: Volume 1 and Bestiary of the Realms: Volume 2 are very long and include non-Maztica monsters. Do you think that Eric L. Boyd and Thomas M. Costa would consent to shorter section 15 entries that only mentioned the monsters that were being included?
Having had another look at this, I'd say that a PDF is possible now, but there are a few things that would make it a great PDF:
1) Monster artwork. Fan artwork for all of these monsters would help flesh them out. (The Candlekeep Forums might be a good place to find artists who are fans of Maztica.)
2) A Maztica/FRCS house style. A house style that people could identify with Maztica and/or Forgotten Realms would help sell this. (The Candlekeep Compendium house style might also work for this project.)
3) Maztica-style cover art. (Check out the
Adlatum Sourcebook to see how great a freebie PDF can be. Again the Candlekeep fans can help with this.)