You can clone with
HTTPS or Subversion.
If I needed to create a new Rails app using an older version I used to just do:
rails _3.1.0_ new myapp
(So using the functionality in the bin wrapper that Rubygems automatically provides).
Since the rails bin was removed from the rails gem on 3.2 I can no longer do this since older versions of railties don't provide the bin in the railties gem (which is the gem the Rubygem's wrapper will look in).
BTW, I realize that you guys may just decide it is not worth fixing. So as a note for anybody in the future you can create your own wrapper (like the one Rubygems generates). Just copy the Rubygems one and replace the bottom with:
# Try the new railties location first
gem 'railties', version
load Gem.bin_path('railties', 'rails', version)
rescue Gem::LoadError, Gem::GemNotFoundException
# Revert back to the old rails location
gem 'rails', version
load Gem.bin_path('rails', 'rails', version)
Yeah, we were aware of this but we had to do such change for those depending on the railties gem.