Ther are no specific statistics on this type of questions but you could make it to plus 20 thousand plus as there are supporters who attend games and those who are followers of the game and this club via TV matches
Leinster Rugby was created in 1875.
Leinster Rugby was founded in 1875 in Ireland and formed from four Irish Rugby teams. Leinster Rugby is responsible for Rugby Union throughout the Irish province of Leinster.
Leinster
On a regular basis about 10 thousand but there are of cousres TV supporters who cannot get to the grounds
... Joe Schmidt: Head Coach
3 million worldwide. but have a lot of watchers
Brian O'Driscoll would be Leinster's best player. He is also regarded as Ireland's best player and one of the best in the world.
Leinster v Munster at Croke Park - 82,208 is a new world record attendance for a club rugby game
The only place to get that signed is to contact the Marketing manager at the club and/or go there on match days and ask for autographs
You will need to be part of the squad or part of the development process through their academy
Leinster are the top selling. Followed by Munster.
Either ebay or contact Leinster marketing team direct and they may have stock still on shelves. However, this is rare to hold old stock