Don't even think about trying to fit a Renault 5 kit, it won't happen unless your a specialist who gets paid to do that kind of thing. Far too much work is involved, and a lot of bodging.
As for that online seller who does the body kits as mentionned before it's in the sticky about online sellers, it's pretty easy to find to be honest, but just so I can't be called petty this is the link
http://www.edworthys.co.uk/. But seriously most of the bits look a bit naff and as for the ones that do look alright well I hope you got money to burn because the plastic will cost more then the Panda.
If your really really set on full blown modding, then sell the Panda and buy something a bit better suited to being modded because trust me you won't find a Panda at your average cruise (famous last words) and there are many really really good reasons for this.
If your just trying to raise your Panda's street cred because your worried about getting laughed at by your mates then take a look at Sprox's and Alan.D's pandas, they are nothing to laugh at and show a Panda at it's best.
It's your car though just be careful you don't end up on barry boys.co.uk
BTW have you named it and driven it yet?