Maybe you installed python from source. In this case, you can recompile python with tcl/tk supported.
/home/xxx/local/tcl-tk/
.# install tcl
wget -c https://prdownloads.sourceforge.net/tcl/tcl8.6.9-src.tar.gz
tar -xvzf tcl8.6.9-src.tar.gz
cd tcl8.6.9
./configure --prefix=/home/xxx/local/tcl-tk/
make
make install
# install tk
wget -c https://prdownloads.sourceforge.net/tcl/tk8.6.9.1-src.tar.gz
tar -xvzf tk8.6.9.1-src.tar.gz
cd tk8.6.9.1
./configure --prefix=/home/xxx/local/tcl-tk/
make
make install
# download the source code of python and decompress it first.
cd <your-python-src-dir>
./configure --prefix=/home/xxx/local/python \
--with-tcltk-includes=/home/xxx/local/tcl-tk/include \
--with-tcltk-libs=/home/xxx/local/tcl-tk/lib
make
make install