When you are in the career mode menu, scroll down and click on Scouting. When the Scouting menu opens up, scroll down and click on Budget Allocation. Scroll all the way to the bottom and press
From the Career menu, scroll down and click on Scouting, then click on Japan Bidding. You will now see the names of the players that you can bid on. Press on their name to bid on them and then set what price you think is good. It is best to set a very high bidding price so you can win. Once you win the bid for a player, you will have to sign them to a contract.
You will not be able to get all 20 in one season, so it is best to get this while you are going for the 30 year career achievement. on Japan to invest scouts there. You will now receive updates when Japanese players want to play in the MLB and you will have the chance to bid on them. You will get these notifications at the end of the postseason, most likely, and you will have to bid on them.