So OK, that's a clue. I know Harimoto had 3085 hits but off hand I didn't know how many wins Koyama had. So I did a quick search for Koyama on Baseball-Reference and did a double-take:
"Last played for DET"? Wait...what?
Clicking on Koyama's page revealed (in addition to confirming that Koyama had 320 wins) that Koyama had pitched 3 innings in one game for the Detroit Tigers Florida Instructional League team in the fall of 1967. A little more research revealed that there were three other Japanese players on that team as well.
Now I had known that there were Japanese players with a couple of the Giants Arizona Instructional League teams in the 1960's but I hadn't realized that there were other teams who hosted NPB players as well. So I started going through all the teams that Baseball-Reference had data for in both Florida and Arizona and came up with a few more. The Washington Senators hosted three Chunichi Dragons in the fall of 1965 with their Florida team. In 1966 there were three teams with NPB players - the Dodgers in Arizona had three players from the Yomiuri Giants while in Florida the White Sox had two players from the Sankei Atoms and the Tigers had two players from Chunichi. The Tigers hosted four players (including Koyama) from the Tokyo Orions in 1967 and four players from two different teams (the Orions and the Nishitetsu Lions) in 1968.
Here's a table with all the players
|1965||Florida||Senators||Tatsuhiko Kimata||Chunichi 1964-82||All Star 1970-71, 1974-75, 1977-80; Best 9 1969-71, 1977, 1979|
|1965||Florida||Senators||Morimichi Takagi||Chunichi 1960-80||CL Stolen Base Leader 1963, 1965, 1973; All Star 1966-67, 1973, 1979; Best 9 1963-67, 1974, 1977; Golden Glove 1974, 1977, 1979; HOF 2006; Meikyukai member, managed Chunichi 1986, 1992-95, 2012-13|
|1965||Florida||Senators||Tatsumi Yamanaka||Chunichi 1962-70||CL Winning Percentage 1963, 1965; All Star 1966|
|1966||Arizona||Dodgers||Chiyosaku Hayashi||Yomiuri 1966-69|
|1966||Arizona||Dodgers||Takeshi Ueda||Yomiuri 1964-78|
|1966||Arizona||Dodgers||Takashi Yoshida||Yomiuri 1964-84||All Star 1976-77|
|1966||Florida||White Sox||Tadakatsu Takayama||Kokutetsu/Sankei/Yakult 1963-70, Hanshin 1971|
|1966||Florida||White Sox||Kunimitsu Yanoura||Kintetsu 1960-65, Sankei 1966-67, Yomiuri 1968||All Star 1963-64, 1966; Played for Tokyo Dragons of the Global League in 1969|
|1966||Florida||Tigers||Isao Hirono||Chunichi 1966-67, Nishitetsu 1968-70, Yomiuri 1971-73, Chunichi 1974||All Star 1969|
|1966||Florida||Tigers||Hiroshi Shintaku||Chunichi 1966-78||All Star 1967|
|1967||Florida||Tigers||Reiji Iishi||Tokyo/Lotte 1965-71, Hiroshima 1972-73||All Star 1966|
|1967||Florida||Tigers||Takenori Ikebe||Daimai/Tokyo/Lotte 1962-1974, Hanshin 1975-78, Kintetsu 1979||All Star 1967, 1969-71; Golden Glove 1972, 1976|
|1967||Florida||Tigers||Masaaki Koyama||Osaka/Hanshin 1953-63, Tokyo/Lotte 1964-72, Taiyo 1973||CL Leader Wins 1964, Winning Percentage 1962, Strikeouts 1962; All Star 1957-60, 1962-67, 1970; Sawamura Award 1962; HOF 2001, Meikyukai Member|
|1967||Florida||Tigers||Hiroyuki Yamazaki||Tokyo/Lotte 1965-78, Seibu 1979-84||All Star 1969-70, 1972-77, 1980-81, 1983; Best 9 1969-71, 1974, 1980; Golden Glove 1977, 1980-81; Meikyukai member|
|1968||Florida||Tigers||Masayoshi Higashida||Nishitetsu/Taiheiyo Club 1968-74, Nippon Ham 1975, Hanshin 1976-77||All Star 1971-72|
|1968||Florida||Tigers||Kazuto Kawabata||Tokyo/Lotte 1967-70, Chunichi 1970, Hiroshima 1974-76, Hankyu 1977-78|
|1968||Florida||Tigers||Mitsuo Motoi||Nishitetsu/Taiheiyo Club/Crown Lighter 1967-78, Taiyo 1979-84||All Star 1968, 1971-73, 1977, 1980; Best 9 1972, 1980; Golden Glove 1980|
|1968||Florida||Tigers||Yasuo Otsuka||Tokyo/Lotte 1966-72||Listed in Baseball-Reference's page for the team as "Yashsheo Otsuka"|
This is a pretty impressive list of players. Out of 18 players, 13 were All Stars at least once. There's also two Hall Of Famers and three Meikyukai members (which includes the two Hall Of Famers).
As you would probably guess there are no known baseball cards of any of these guys while they were with their respective Instructional League team. Most of them have had baseball cards in Japan - I have cards of 12 of them:
|1979 Calbee July Best #30 (Kimata)|
|1975/76 Calbee #446 (Takagi)|
|1967 Kabaya-Leaf #54 (Yamanaka)|
|1974 Calbee #359 (Ueda)|
|1973 Calbee #27 (Yoshida)|
|1960 Marusho 4 In 1 B&W (JBR6) (Yanoura)|
|2009 Epoch All Japan Baseball Foundation 15th Anniversary #15|
|2016 BBM Dragons 80th Anniversary #10|
|~1966 Mel Bailey Postcard (Koyama)|
|2010 Epoch 1977 #37|
|2011 BBM Lions Classic #50|
|1978 Yamakatsu JY6 (Motoi)|
As far as I can tell Ikebe is the only one of the other six players who ever had a baseball card. He has two cards in the 1974/75 Calbee set.