Well there should be forum software to take care of this (c.f. threaded view), since there is a natural link between the quoting post and the quoted post. When poster quotes a post, add link to new post's number (the # in the top right corner of each post) to the old post.

Each post could contain this:
Quoting posts:
#4
#75
#82
(formatted in a nice way, there should be space for this)

So what I mean is to implement the feature in the forum, not require each poster or a moderator to do it manually.