Why don't you just publish them yourself? A short text-only story is very easy to format and upload. Read NJ's blogposts about things to watch for in Word, and you're on your way.
Alternately, you could try the traditional SF magazines, though they're hard to get into. They certainly pay better than KDP!
I have the impression that your shorts have never sold well on KDP. That unfortunately is true for most authors (erotica may be an outlier). Have you considered bundling them into longer books built around a single theme or universe? Good luck!
It occurs to me that if you're switching pen names all the time, you may be hampering your sales. Someone who likes your stories won't know that a different pen name is also you. You don't need a separate pen name for every different story or group of linked stories! Look at the best known and most successful SF/F writers, people like Larry Niven or Lois Bujold or Orson Scott Card. They wrote all different kinds of stories but stuck with the same author name.
The only time you'd want very different pen names would be if you knew you wouldn't want readers of one group of stories (happy bunny stories for kids) accidentally getting very different stories (racy adult escapades).
You can publish on Kobo and Nook all by yourself. It's no harder than getting onto KDP. It is harder getting onto iTunes. For that you'd need an aggregator, unless (like me) you work with a Mac and enjoy a challenge. But just use one of your regular author names for SW.