At first glance the current behaviour is correct:

1) Bundles aren't shared libraries, but plugin code. It should be 
possible to load bundles, but I don't agree that find_library should try 
to locate them, specially given this bit in the documentation:

[quote]
The purpose of the find_library function is to locate a library in a way 
similar to what the compiler does (on platforms with several versions of 
a shared library the most recent should be loaded), while the ctypes 
library loaders act like when a program is run, and call the runtime 
loader directly.
[/quote]

2) There is no prescribed suffix for bundles. Python uses .so and some 
other packages use .bundle, but that's just a convention that a specific  
software product chooses.