I have indeed a huge collection of logos mainly in iff/ilbm format. They are (for the most part) named with author/name /date (if found) of piece. Imho, i warn you about being too confident about png, mainly because png format do not record amiga screen mode (lores, half-brite, laced and so on...) utilized by the picture. proggies like Xnview read and manage iff/ilbm without problems (though there are occasionnal glitchy pics which need to be loaded/resaved by dpaint or brilliance).
I would be happy to share these pics with you, amiga gfx preservation is one of my hobbies!