You can download source code tarball from here.
You can checkout source code from Subversion repository:
Checkout over SVN protocol (TCP 3690):
svn co svn://svn.gna.org/svn/a2jmidid/code a2jmidid
Checkout over http:
svn co http://svn.gna.org/svn/a2jmidid/code a2jmidid
Feedback
If you find have trouble getting a2jmidid working, found a bug or you miss some feature, please submit support request here.
Other useful info
This project is hosted by Gna!. Gna! project page is here. a2jmidid is written and supported by Nedko Arnaudov. a2jmidid is based on jack-alsamidi-0.5 (jackd alsa seq midi backend) by Dmitry Baikov. You can reach me at nedko (a.t) arnaudov (dot) name. I can also be found in #lad on FreeNode (as nedko).