Hmm... well:
First: The topic you were talking about (This one), it's basically what you are asking for("an archive like the Pokemon Location guide, but for different/personal custom shinies"). It's just "not official" for a lack of a better term. Also, it's not everyone that wants to change shiny sprites. Most people will accept the shiny the way they are/will be. If you know how to change the game sprites, feel free to do so. It's not like anyone can stop you.
Second: "and I saw many good ones that, sadly, were rejected" - Well... expected? After all, there are 719 (confirmed) pokemons. People can make over a million sprites, and only one will be picked in the end anyway, cuz afaic, a pokemon can't have multiple shiny sprites. So... yeah. Good sprites will be left behind, because there are better ones. Which brings me back to the first point: "If you know how to changes sprites, do it."
To sum it up: I don't think people are "unhappy" with the custom sprites we have right now. And if they are, they aren't saying anything about it.
And keep in mind that the custom sprites thing is far from over. The 1st Gen custom sprites were finished in June, and the 2nd Gen custom sprites topic is still open, which means there's a lot of work to do. You might as well read the topic and see what you can edit, how or present a different idea maybe. I believe it would be appreciated.
And last thing: I like that Weavile, can i haz it?