This one can be found in the Diablo SDK repo. The structure of dists is
different though. I can see it in my Diablo with N800 in redpill.

Details:
Catalogue Name: Maemo Diablo
Web address: http://repository.maemo.org/
Distribution: diablo
Components: sdk/free tools/free sdk/non-free tools/non-free

Or (not tested), these lines in your sources.list[.d]:
deb http://repository.maemo.org/ diablo/sdk free non-free
deb-src http://repository.maemo.org/ diablo/sdk free
deb http://repository.maemo.org/ diablo/tools free non-free
deb-src http://repository.maemo.org/ diablo/tools free