I think it's not possible because:
300 books/month means 10 books/day. Let's be realistic and say that a writer needs 10 days to write a proper short story.
So, you have to give the order for 10 books to 10 authors today, to get the results (10 books) at the 10th day. Tomorrow you have to hire 10 authors more, to get the results (10 books) at the 11th day. And so on. To get in a "flow" in which you're getting 10 books every day, you need 10 × 10 writers = 100 writers totally.
Additionally you need:
- People who are writing the outlines (For 10 outlines/day, I would say you need 2 people for this task)
- 2 Cover designer
- 3 people for editing/proof reading the stories
- 1 person who's managing everything
- 1 person who's writing the description and upload everything.
Costs: ~$50k/month minimum
Conclusion:
I can't believe that there's a company that has 100+ employees (who have nothing to do), to work for a single customer exclusively. It needs time to build up such a huge team, teach them what they've to do etc. and would be too risky if the customer (you) jumps off someday.
Try to hire and work with 10 authors + cover designer etc. and you'll reach your personal limit quickly. + People are no machines. They need breaks, weekends, sometimes they're lazy. So, if the the writers are not fast enough you have less work for your proof readers or cover designers. But you have to give them enough work constantly to bind them exclusively to you. Otherwise they'll look out for new jobs. This is a risk because maybe next week your authors are very fast but your cover designer has less time because he has other jobs to do. To bind someone exclusively to you is important to get stability but that means that you have to pay them sometimes even you've not enough work.
In the theory it's very easy to say: Currently I'm able to publish 10 stories/month and make $1.000€/month. If I scale it up to 300 stories/month I could make $30.000/month. But that's not how it works practically.
So no, there isn't a company who has built up such a big business structure and waiting for you. And I guess there's also no company who'll build up such a structure (with all its risks) for you.