python2.7 can be build from AUR.
Using AUR also implies using Manjaro’s edge branch (unstable) - not that unstable - it is actually Arch stable.
So the short version is
sudo pacman-mirrors -aS unstable
sudo pacman -Syu git base-devel --needed
git clone https://aur.archlinux.org/python2
cd python2
makepkg -is
The longer version → see [Need-To-Know] About Manjaro and AUR