Install specific package version (available on Launchpad)

I'm trying to pin packages installed through apt on Ubuntu 20.04. Unfortunately older versions of packages are removed very quickly it seems, so e.g.:

apt install -y git=1:2.25.1-1ubuntu3.6

yields:

E: Version '1:2.25.1-1ubuntu3.6' for 'git' was not found

I can see this exact same package version on Launchpad: https://launchpad.net/ubuntu/+source/git/1:2.25.1-1ubuntu3.6 and I can download the .deb file and install it.

How can I tell apt to search on the Launchpad repository for this package? Is that even possible? If going to the builds page it seems to be listed under ~ubuntu-security which is a private PPA which I cannot add:

# add-apt-repository ppa:ubuntu-security/ppa
Adding private PPAs is not supported currently

(But I'm not sure if I'm using this correctly).

Launchpad's historic library is not an apt-compatible repository. Nor can it be made so by user actions.

There are no known tools to make Launchpad compatible with apt. (That would be a support nightmare!)

You must manually browse and download the debs you want.

While trying to find a way around this I found that Debian maintains snapshots of their complete package repository (e.g. http://snapshot.debian.org/archive/debian/20230804T031641Z/). You can add this snapshot as a source for apt - and this should (I believe) always lead to the exact same packages being installed:

echo 'deb [trusted=yes] http://snapshot.debian.org/archive/debian/20230804T031641Z/ bullseye main' > /etc/apt/sources.list.d/snapshot.list && \
    printf "Package: r-*\nPin: origin snapshot.debian.org\nPin-Priority: 990\n" > /etc/apt/preferences.d/snapshot && \
    apt -o Acquire::Check-Valid-Until=false update

When now doing apt install -y curl this should always get you 7.74.0-1.3+deb11u7.

Unfortunately Debian snapshots are (in the short time that I've been testing it) have been very slow and unreliable; so it would be great if someone would make a commercial version of this.