How to get all dependent source packages

[sha liu <sandyleo26@gmail.com>]

Hi everyone,
    Is there any easy method to get all the *source* packages which are the build dependency of one package?
    What I want to do is building dpkg from source on a CLFS[0] system. So I have to get all the dpkg's dependency source packages and the dependency of dependency and so on...
    I look into auto-apt, apt-get builddep. Both of them install the binary packages to fulfill the dependency, not downloading the source packages.
     It's
crazy to download all dependent source packages of dpkg, right? Any suggestion is welcomed!

[0]http://trac.cross-lfs.org/
    For those don't know clfs, just think a CLFS system as a minimal linux system without debianization.
--
Best,
Sha Liu