You can clone with
HTTPS or Subversion.
To comply with Debian requirements TKL needs to have a deb-src repo where the debian sources for our custom packages are stored.
Yes, supporting this properly should be high on our priorities. We have all the source in GitHub but that's not as easy as using apt-get source packagename...
I think it would be a good idea to add the capability to build not just binary but also source packages to TKLDev: