Hey your right it is one of my fav. from Penguianl. Here is the link.
http://penguin-fics.livejournal.com/29267.html
Not sure if this is the first one with a link to more or not. Here is the second part to the one above.
http://penguin-fics.livejournal.com/29473.html

http://penguin-fics.livejournal.com/29773.html
http://penguin-fics.livejournal.com/30012.html
http://penguin-fics.livejournal.com/30596.html
http://penguin-fics.livejournal.com/30877.html
http://penguin-fics.livejournal.com/32908.html
If from here on out you can't find the rest please feel free to drop me a line if you need to. I saved them in my fav.

This is one of my best loved numb3rs sties.

If you like Charlie/Billy, Don/Ian here is another one of their stories that I love to read. Other then the Don/Ian/Charlie set that is.
http://penguin-fics.livejournal.com/51311.html