World Cup players by league

On the subject of what leagues/ Clubs based on the original squads

https://en.m.wikipedia.org/wiki/2019_Rugby_World_Cup_squads

Five squads included no players based outside their home country: England, France, Ireland, Japan, and New Zealand.
The squads with the fewest number of players playing domestically are Tonga (zero) and Samoa (one).

Players Clubs
26 Jaguares
20 Welwitschias
16 Benetton,  Glasgow Warriors
15 Saracens
14 Leinster
13 Scarlets
12 Crusaders,  Munster
11 Edinburgh
10 Clermont,  Krasny Yar,  Racing,  Toulouse, Zebre
9 Brumbies,  Melbourne Rebels,  Ospreys, Toronto Arrows

By league
Pro14: 118 19.0%
Super Rugby: 118 19.0%
Top 14 (France): 78 12.5%
Premiership Rugby (England): 74 11.9%
Major League Rugby: 37 5.9%
Top League (Japan): 32 5.1%
Rugby Premier League (Russia): 31 5.0%
Namibia (Welwichtas): 20 3.2%
Campeonato Uruguayo de Rugby: 16 2.5%
Pro D2 (France): 16 2.5%
RFU Championship (England): 13 2.0%
Global Rapid Rugby: 10 1.6%
Didi 10 (Georgia): 9 1.5%
Other: 28 4.5%
Unattached: 20 3.2%