As promised, the art source compilation for April is up on Patreon. It contains all of my recent artwork (from 2013 to 2018) under a CC-BY-SA license (you're free to modify and share as long as you credit and keep the same license). Note that those sources are for GIMP (xcf) and not Photoshop (psd)... if PS can't import them by default, GIMP is free so just download it and convert to another format that supports layers (tif).
This is a 10$ exclusive. It will become public next month, but if you want early access make sure you are in this tier or higher. If you don't plan on becoming a patron now, you may save this link and check it at a later date once the timer expires. Note that this doesn't affect your ability to repost those sources elsewhere: It's only this post that is exclusive, the art itself is CC-BY-SA so you're already free to use these files as you please.