Missing library in Ubuntu 20.04

A package that I want to use needs a shared library called libCGAL.so.13. When I run it, I get the following error:

error while loading shared libraries: libCGAL.so.13: cannot open shared object file: No such file or directory

When I try to install it using $ sudo apt install libcgal13, apt is unable to locate the package.

After some research, I figured that libcgal13 is no longer available in Ubuntu 20.04. And that the last version that still has this package is Ubuntu 18.04.

Can I download this library somewhere without using apt (and just putting the .so file in my /usr/lib/ directory). If not, is there a way to install a package from previous releases ?

EDIT:

Output of grep -r ^deb /etc/apt/ --include="*.list"

/etc/apt/sources.list:deb http://fr.archive.ubuntu.com/ubuntu/ focal main restricted
/etc/apt/sources.list:deb http://fr.archive.ubuntu.com/ubuntu/ focal-updates main restricted
/etc/apt/sources.list:deb http://fr.archive.ubuntu.com/ubuntu/ focal universe
/etc/apt/sources.list:deb http://fr.archive.ubuntu.com/ubuntu/ focal-updates universe
/etc/apt/sources.list:deb http://fr.archive.ubuntu.com/ubuntu/ focal multiverse
/etc/apt/sources.list:deb http://fr.archive.ubuntu.com/ubuntu/ focal-updates multiverse
/etc/apt/sources.list:deb http://fr.archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse
/etc/apt/sources.list:deb http://security.ubuntu.com/ubuntu focal-security main restricted
/etc/apt/sources.list:deb http://security.ubuntu.com/ubuntu focal-security universe
/etc/apt/sources.list:deb http://security.ubuntu.com/ubuntu focal-security multiverse
/etc/apt/sources.list.d/teams.list:deb [arch=amd64] https://packages.microsoft.com/repos/ms-teams stable main
/etc/apt/sources.list.d/sublime-text.list:deb https://download.sublimetext.com/ apt/stable/ # 
/etc/apt/sources.list.d/openjdk-r-ubuntu-ppa-disco.list:deb http://ppa.launchpad.net/openjdk-r/ppa/ubuntu disco main #
/etc/apt/sources.list.d/openjdk-r-ubuntu-ppa-disco.list:deb-src http://ppa.launchpad.net/openjdk-r/ppa/ubuntu disco main
/etc/apt/sources.list.d/ubuntugis-ubuntu-ubuntugis-unstable-focal.list:deb http://ppa.launchpad.net/ubuntugis/ubuntugis-unstable/ubuntu focal main

EDIT 2:

I was able to make it work by compiling the library from source and using ldconfig afterwards as @llywrch suggested.

The package is available in 18.04 LTS repository from universe pocket.

You have to add the repository with:

sudo add-apt-repository universe
sudo apt-get update

And then install the 64-bit library with:

sudo apt-get install libcgal13

If you know that application is 32-bit - use additional command:

sudo apt-get install libcgal13:i386