i just upgraded to ubuntu studio 16.04 and noticed that pd extended was gone
came across this message in syanptic when trying to install it again
"pd-extended:

Package pd-extended has no available version, but exists in the database.
This typically means that the package was mentioned in a dependency and never uploaded, has been obsoleted or is not available with the contents of sources.list
"

I guess the Ubuntu repositories have been updated recently? Since Pd-extended has been officially declared "not maintained", they might have removed it from their repositories for this reason. Why don't you go for vanilla? Since it now includes the deken-plugin for installing externals really easily, there's no reason why you shouldn't.
Even if you don't want to compile yourself, the Ubuntu repositories are very likely to include a new version (you need >= 0.47-0). The Debian repositories have been updated, that I know for sure.

Nope, Vanilla is gone from the repository as well. You have to download it and compile it from Miller's site. Really bad that this hasn't been updated.