Copy and paste is your friend. Write something in notepad like "Hi, need one more for foundry if you're interested" (keep it as polite as possible). Copy what you wrote. Open who menu and do your level range search. Now go down the menu and right click - whisper, control v, right click - whisper, control v, right click - whisper, control v and on and on and on.
This works every time, usually only takes a few minutes. If you're looking for something specific like a tank, just do a level range search and sort by class and spam the tank classes.
I used to do this ALL the time on LOTRO as well.
I think maybe 2 times someone got pissed, but if someone's going to get mad about 1 whisper I wouldn't want to group with them anyways.