If you don't mind sharing which 3rd party stores do you have success with? I have tried Amazon with pretty much no success so I've assumed if they can't do it no one can.
We are in Samsung store (roughly same performacne as google play), several carrier stores (separated they are tiny, summed they are a good income), and we have some deals with some startups that are trying new app distribution methods, many of those startups also have deals with carriers, so we are in some carriers twice.
Anyway, our income right now looks like as if it came from dumbphone era: most of it coming from carriers, directly or indirectly.
Also we are in Yandex store, nothing impressive in terms of revenue, but stupid easy to get into (they purpusefully allow use of google play APIs, and upload methods, and whatnot... if you ever worked with google play, uploading to Yandex is VERY easy).
EDIT: Making things clearer on Amazon, they are REALLY the worst, sometimes months go by without even a single free download.
I remember finding your games here on HN quite some time ago, my 3 year old can now do your animated jigsaws herself and currently loves the game with the russian dolls. My email in my profile is also my Skype if you want to chat, maybe we can help each other out - all my downloads are for traditional jigsaws and an older audience, with children and grandchildren.
