Damn. It's about time someone brought up the RPSNL.
Brilliant, you are correct in that most of the information about the Leagues survive only in oral form, however my Great Aunt Genevieve has some old pictures that you are more than welcome to puruse while you're in the DC area (hit me with a PM.) The information below is triangulated from the many stories about the Leagues I remember from my youth. Many of the stories were of the inspirational variety, serving to fill the heads of us young players with glorious tales from the League's Golden Years. I will attempt to restrict my commentary to matters of fact, more or less.
The roots of the RPSNL go back to at least the Civil War (further back, actually, as the game itself comes from Africa, a fact now recognized by all RPS historians.) During the Civil War, RPS tournaments were held in many different Southern cities. Then as now, the promoters of these tournaments were sympathetic to humanitarian concerns, and used the events as a kind of "Underground Railroad." Many of these players, who learned the sport while in Africa, made it all the way up the Railroad to Canada. Quite a few of them settled in Toronto, which explains why RPS is still so strong there today.
The Negro Leagues are correctly termed in the plural, for there were many of them. These included such Leagues as the Mississippi River RPS League, the Zulu Nation League, the Tarheel League, the Friends of RPS, the Memphis Eclipse, and the Atlanta based Huck-a-Buck League. Historically, the very first League was in the late 1800's; it failed after a month. Many of those later groups reached their peak in the late '20s. The players were well known, and were making more money monthly than many others in their respective cities, white or black. This success continued into the 1930's and 1940's. With the onset of WWII, many well-known Black players joined the war effort, which eventually led to the more widespread removal of segregated RPS Leagues.
This segregation initially mirrored society as a whole. Just as there were "white" restaurants and "Black" restaurants, so there were "white" RPS Leagues and "Black" RPS Leagues. Well, at least in theory. My grandfather tells me that although no Black player could be seen at a white RPS tournament, many well known white players were known to appear at Black tournaments. Notable among these was the late Simon "Old Timer" Watson, Sr. He travelled the entire RPSNL circuit, and was a friend to many top players and promoters. Time and time again, according to my grandfather, he was invited to compete in the tournaments, but refused. As he explained it, "My people won't let any of you compete in their tournaments, so I don't think I have the right to compete in yours. I'm just happy to be here." Watson went on to become involved in the civil rights movement in the 1960's.
There were quite a few well known players in the Leagues. Carolan Trimestus of the Huck-a-Bucks followed the familiar "player/promoter" mold in use today, and was renowned for his fast-prime ability. Abraham Walker of the Memphis Eclipse once came in second place in three consecutive tournaments of over a hundred players (but ironically, never won a tournament!) Frank Foster of the Philadelphia City League (no relation to Mr. Urbanus' League of the same name) was a fantastic organizer during the fallout period of the late 50's. He insisted that all Negro League promotions be run by Black entrepreneurs; given the large amount of money the Leagues were making at the time, he rightly considered that the money should stay in the community. Rube "The Barber" Leland carried his barber shears with him during tournaments, and would sharpen them maliciously between matches. Bruce Brownlee was a notorious numbers runner and gangster, as well as owner of the Pittsburgh Playboys RPS League. He was immortalized by Langston Hughes in his poem "Bruce Brownlee is after Me":
Bruce Brownlee is after me
He already owns every cent I ever had
They say Bruce is loose as a goose, and I guess they're right
But I wish he'd be looser with my money
My dreams have been deferred
But Bruce won't defer the five dollars I owe him from Monday night's rochambeau
Rock, you let me down. Feet, keep runnin'
There were several famous players who dabbled in the Leagues, but the only one to achieve respect as a player was singer Wynonie Harris of "Bloodshot Eyes" fame. Harris would arrange tour dates to coincide with major RPSNL tournaments, and typically would emerge in the final eight.
The big question mark is how the Leagues were actually organized. Clearly, between the late 20's and the early 50's some sort of coalition was made to standardize rules and rankings across the Leagues, but I know nothing about how this happened. Hopefully, the names I've given you will help you find what you're looking for.
My compliments and congratulations again on beginning this fascinating area of study. I look forward to any new information you may uncover.