I thought I did. Anyway, I did again, and fared a little better, but failed on the patch command (No such file or directory).
$ apt-get source libsane1
Reading package lists... Done
Picking 'sane-backends' as source package instead of 'libsane1'
NOTICE: 'sane-backends' packaging is maintained in the 'Git' version control system at:
git://anonscm.debian.org/collab-maint/sane-backends.git
Please use:
git clone git://anonscm.debian.org/collab-maint/sane-backends.git
to retrieve the latest (possibly unreleased) updates to the package.
Need to get 6,545 kB of source archives.
Get:1 http://archive.ubuntu.com/ubuntu bionic/main sane-backends 1.0.27-1~experimental3ubuntu2 (dsc) [2,495 B]
Get:2 http://archive.ubuntu.com/ubuntu bionic/main sane-backends 1.0.27-1~experimental3ubuntu2 (tar) [6,430 kB]
Get:3 http://archive.ubuntu.com/ubuntu bionic/main sane-backends 1.0.27-1~experimental3ubuntu2 (diff) [112 kB]
Fetched 6,545 kB in 1s (4,371 kB/s)
dpkg-source: info: extracting sane-backends in sane-backends-1.0.27
dpkg-source: info: unpacking sane-backends_1.0.27.orig.tar.gz
dpkg-source: info: unpacking sane-backends_1.0.27-1~experimental3ubuntu2.debian.tar.xz
dpkg-source: info: applying 0020-nousbtest.patch
dpkg-source: info: applying 0025-multiarch_manpages_libdir.patch
dpkg-source: info: applying 0035-trim-libraries-in-sane-backends.pc.in.patch
dpkg-source: info: applying 0600-scanimage_manpage.patch
dpkg-source: info: applying 0705-kfreebsd.patch
dpkg-source: info: applying 0710-sane-desc.c_debian_mods.patch
dpkg-source: info: applying 0140-avahi.patch
dpkg-source: info: applying 0145-avahi.patch
dpkg-source: info: applying 0100-source_spelling.patch
dpkg-source: info: applying 0150-genesys-Fix-use-of-uninitialized-variable.patch
$ patch sane-backends-1.0.27/backend/genesys.c --dry-run < genesys.c.diff
bash: genesys.c.diff: No such file or directory
$