How to replenish minor leagues
 

The annual rookie draft is only going about 6 players deep, even though it's set for 20. How do I get more players into my minor league system?

you could add more rounds to the draft. That's under league setting > amateur draft. Click the box to allow the draft to take place. Then you can change the number of players in each round and as well as the number of rounds. Hope this helps. Another way to get more players, is through the international amateurs .... (that's under league setting >players.) They will pop up at various times, but you need scouting activated and have a scouting coach for that work I believe.

Unless you want to introduce fictional players into the league, you will have to use ghost players to fill out the minor league rosters. You can introduce fictional players and check the box to block them from ever reaching the majors.

I usually prefer reserve rosters in my historical leagues, instead of fictional players or empty minor league teams. There are no options or waivers in this type of setup, which might be good or bad depending upon your point of view.