On my Raspberry Pi computer I did a search for PIL and matplotlib with
apt-cache search python
but could not find anything close in the list.

Is PIL/Pillow and matplotlib available for Linux and what is it called?

The Raspberry Pi has Python27 and Python32 installed.

On my system it is

sudo apt-get install python-matplotlib python3-matplotlib python-pil python3-pil

It is easier to find packages with aptitude

sudo apt-get install aptitude
aptitude search pil

In Kubuntu, aptitude says that the new python Pil is a fork of Pillow.

It is my understanding that pillow has basicly taken over the further development of PIL.