It can be hard to "fit in " when u 're the new guy. and esp to fit into already established relationships.
Note though that although he might feel that every one has a pal. remember as well in the larger companies most of these are really only acquaintances.
I'd say see if there is a social mixing outside the workplace ie there might be team bonding ie pub outings etc that he could go to . and also as earlier postings said there might be a sports and social club as well due to the size of the company ie 600 employees that he could join that would have poss sports activities. His manager or HR would be able to advise of that or there might be a company HR website that gives those details
3 Weeks though is'nt really enough to judge the place. if it really is that insular . Note he would have to understand that in some instances, and i dont mean all and i'm coming from a womans perspective on this, that sometimes in an all female environ. it can get fraught with emotion and maybe when he gets to know some of these so call colleagues he might see that they are not really that interesting to spend his breaks with anyway .
In my workplace here, i have been here over 5 years but i was out sick for 8 months , when i came back , most of the original crowd had left on my team in that time period, (high turnover of staff in our comp ) and i felt like the beginner the newbie when i came back too, and there were some girls that had i guess their own clique that i did'nt feel part of - ie conversations and exclusion . however i found out afterwards that they were'nt the most popular and rubbed others up the wrong way too , but no one really wanted to say it to their faces.
in the end i came in ,did the best job i can , and just because i had to put on a brave face showing i did'nt care. Now the ring leader has been promoted to another department (great !) and the group dynamics is a way better.
maybe he could have a friendly word in his managers ear, do the teams have any nights out as bonding so he can get to know the group in a more relaxed environment (poss company might pay for it ! )