Which API is this? You’ll need to provide more information to aid in troubleshooting. This also includes how you have installed it and set up your Rhino/GHPython/Python paths etc. etc.
As far as I can tell: this is NOT a standard Python module, you may therefore simply need to install it (i.e. ensure that all the etabs dependencies are installed correctly). Note that it depends on ctypes, which is in fact usable from IronPython, and IS part of the (Iron)Python Standard Library. That said, you may be looking at quite some dependency hell here, but I wouldn’t give up.
The Standard Library for CPython and IronPython are actually more or less identical. I assume you are referring to things like numpy, which is also not part of CPython. Maybe be more specific about things like this, prevent them fake python news from spreading.
I’d suggest trying the same if installing comtypes fails, since it is already working in your external CPython interpreter. There are these two options currently (that I know of):