First...if your going to replace 3 then you might as well replace ALL of the injectors....You are going to have to dismantle the whole thing so while you have it apart change ALL the injectors and install NEW o rings
This site can answer injector questions....and has several options for injectors
http://www.fiveomotorsport.com/Injector_Sets.html
JUST MAKE SURE YOU LABEL THE CONNECTORS FOR THE INJECTORS BEFORE YOU DISCONNECT THEM.....