If you mean the shelf behind the rear seat there is one on Ebay now, if you're quick:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&category=10382&item=2479518088&rd=1&ssPageName=WDVW
appears to be new but only 2 hours to go, currently 15UKP, one bidder.
I think I've seen lock mechanisms on there recently, but can't find one at the moment.
There maybe someone along in a while who has one saved from a scrapped Panda...
Doors are another matter - almost without exception they rust.
PandamanPaul has had a garage repair done on his recently.. others (like me) mess about with filler, etc... but it's usually just a matter of months before it bubbles through again.
BTW, what colour is your Panda??