You'll have to be creative and do some research
Mh first step would be locating a competitor
And find who is the manufacturer and track them
Who is the distributor and track them
And then just benchmarking that into finding opportunities
This path isn't something you'd want to hire a fiverr consultant for, this path is a bit specialized into logistics if you want to grow it
Actually you should go into another subreddit
I'm not sure what you think of "passive income" is
You need to create something that would be sold, either that or a scam