Why can't pip find pysvn?

As it turns out, because I didn't use pip install for pysvn, pip didn't know that pysvn existed. Because it wasn't available from PyPI (the Python Package Index), there was no way that pip could see it (because that's where pip goes first to find packages that it's attempting to install).

From the pip user guide:

pip supports installing from PyPI, version control, local projects, and directly from distribution files.

Since I had eventually downloaded pysvn from its own download site (which was not any of the above 4 options) and ran the .exe manually, pip simply doesn't know about it even though it's in the same directory as other packages installed by pip.

I suppose I could've also retrieved the distribution files and used pip with those, but my workaround did the trick.