The DD-WRT forum is definitely a better place to find people who are experienced with doing this and get advice related to rolling your own firmware.
For your specific model, the flashing process is outlined briefly and discussed in this thread.
More detailed steps can be found on the wiki page for your model here.
lightsword hosts many versions of Linksys firmware source code on his sourceforge page here.
As I'm sure you are already aware, flashing you firmware always comes with some level of risk. You should carefully review all instructions, warnings, and related discussions before attempting the steps outlined on the pages linked above.