In his own words:
"The AD zip file is getting a bit big and inconvenient to download and I think its time to start splitting stuff off into separate files. The AD map source files are not needed or viewed much and if anyone wants to see them, just drop me an email request.
This download contains all the previous maps, some new extra code and features, lots of bug fixes, some new mapper features (check documentation) and as a final bonus, a couple of extra maps hidden away in the main map hubs, good hunting!"
Those two models showed up in TB2 as missing, and when I place the monster_boil it doesn't show up in game either. (I'm assuming it's meant to - I don't really know how it works :/)
They're not in my .zip that I downloaded either, so I don't think I screwed up extraction.