docker source package

I am trying to download docker source packages on ubuntu 19.04 but apt-get update fails with the following error: : Skipping acquire of configured file ‘stable/source/Sources’ as repository ‘ disco InRelease’ does not seem to provide it (sources.list entry misspelt?) root@kallol-OptiPlex-9020:~#

The file /etc/apt/sources.list:

 # This system was installed using small removable media # (e.g. netinst, live or single CD). The matching "deb cdrom" # entries were disabled at the end of the installation process. # For information about how to configure apt package sources, deb [arch=amd64] disco stable deb-src [arch=amd64] disco stable # see the sources.list(5) manual. root@kallol-OptiPlex-9020:~#  

Any idea?

Alternative, is it possible to download ubuntu docker src package manually?