Ryan has reported in the past on baseball cards related to the league. BBM did cards in at least 2010 and 2011 (no idea how they were distributed) and an outfit called AIAIO has been issuing cards for the league since 2012 maybe although they appear to be either a give away with tickets or possibly sold through AIAIO itself. Last October thought, Epoch issued what I believe is the first national release of baseball cards for the league. It was a 78 card set issued as a traditional pack based set - it was sold in boxes of 20 packs of 5 cards each. It actually was the ONLY set Epoch issued last year as a traditional pack based set instead of a ridiculously overpriced box containing a handful of cards for more than 10,000 yen. There were no insert cards to go with the base set although there were possible autographed cards as well as "checki" cards.
The cards for each team include a card of the mascot, the manager and a coach. There are 22 cards for Hyogo Dione, 21 cards for Kyoto Flora, 13 cards for Reia and 21 cards for Saitama Astraia. Each of the teams has a former NPB player as either coach or manager - Hyogo coach Tomoya Kawaguchi (Orix), Kyoto coach Heisyu Ohhara (Yakult), Reia coach Takanobu Tsujiuchi (Yomiuri) and Saitama manager Shinsaku Katahira (Nankai, Seibu & Taiyo).
I've no idea why Reia has much fewer cards than the other three teams. What's also odd is that Hyogo, Kyoto and Saitama have only one "Rookie" card but Reia has four. Since I don't know anything about the league, I don't know if the player selection is leaving anyone out. I do know that the two players I was aware of - Shingo Kawabata of the Swallows sister Yuki and Minami Takatsuka who had a promo card for the 2015 Real Venus set in SCM #114 - are both in the set.
The cards themselves are pretty attractive and for the most part feature action photos of the players:
You can as always see all the cards at Jambalaya. They have a handful of the autographed cards on line as well.