Canonical used to make the animal mascot available as an .svg on the Ubuntu Wiki, but the page hasn’t been updated since the Zesty Zapus release.
I know I had an .svg of the Artful and Bionic mascots at one point, which I think I found on Launchpad via @willcooke. I’ve not seen any similar mascot files for C or for D, though.
I’m not sure there’s ever been a full SVG release of the stock wallpaper, though?
I know this reply hasn’t been much help, but having the mascot SVG would still be useful. I traced my own vector of the dingo (alas not the cuttlefish, as it was too intricate).