Installation of core emulator : 'tcl8.5' not installing

I'm trying to install core emulator on Ubuntu 20.04 and I came across an installation procedure and it had the following command

$ sudo apt-get install bash bridge-utils ebtables \
  iproute libev-dev python tcl8.5 tk8.5 libtk-img \
  autoconf automake gcc libev-dev make python-dev \
  libreadline-dev pkg-config imagemagick help2man

and executing command I'm getting the following error

Package tk8.5 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

Package tcl8.5 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'tcl8.5' has no installation candidate
E: Package 'tk8.5' has no installation candidate

I tried to install tcl8.5 separately with

sudo apt-get install tcl8.5

and I got the same error What is wrong? Is tcl8.5 obsolete?