I just checked piCore and it looks like you are right: $ tce-load -i python2.7 tk
$ python2.7
>>> import sys
>>> import Tkinter as tk
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/local/lib/python2.7/lib-tk/Tkinter.py", line 39, in <module>
import _tkinter # If this fails your Python may not be configured for Tk
ImportError: No module named _tkinter