I've actually ripped apart my car similarly to what you are describing, and I had to get a new carpet because mine was very disturbing. I got my carpet from http://www.stockinteriors.com/
, and it came in preformed. I think it'* either just as good as new or even better! It even comes with (perhaps asbestos) padding at the foot resting areas. The only "thing" about it is that it had no cuts for the center console or seat stud holes. Those were taken care of by a friend of mine while I handled other matters, but it seems easy enough. He just used a pair of surgical scissors.
As for the plastic bits and pieces, take the many types you have to auto stores like NAPA, Advance Auto Parts, Auto Zone, etc., and ask them for their packets of such plastic retainers and clips. Auto Zone has their plastic clips in bulk in boxes hanging off a display at an aisle end, usually.