From the late 1970s all the way until 1997, the only cards produced of sumo wrestlers were playing cards, or trump cards as they are called in Japanese. It wasn't until 1997 that BBM produced regular sumo cards and distributed them on a wide scale to collectors. So for 20 years, collectors had to suffice with these annual releases(still confirming if these were released every year or every few years). It's not surprising though as the end of the mini card, bromide, and menko boom of the 1970s had petered out by the time the great Yokozuna Chiyonofuji became popular in the early 1980s. So for the extreme collectors we have to make due with the playing card sets to bridge this 20-year gap.
The playing card formats have stayed relatively the same since the first known set was produced in 1976. Even the back design has stayed the same sans the late 1980s and early 1990s sets which featured a picture of the new Kokugikan on the back card face. They eventually reverted back to the old design, though. The early sets did not have the wrestlers name in English at the top, but soon included it and it has been standard ever since. All sets feature 52 of the most popular wrestlers at the time the set was printed as well as a joker card of the gyoji (referee).
Right now there are confirmed sets for the following years:
Surprisingly, these sets are actually extremely difficult to find and only ~6 or sets pop up every year. Older sets often command $50 while some of the new sets can easily be had for $5-$10 on the secondary market. These set new were sold at the tournaments for about 1500円 and can still be purchased today during tournaments!
This 2009 set is one that I recently cataloged and is unique in the fact that it is the first set that I know of to feature two gyoji on the same card. It also has 4 of the modern day Yokozuna in it (Asashoryu, Harumafuji, Hakuho and Kakuryu).