I got mine from Evilbay, just type in "white wall tyre trims".
There's two methods of fitment, either pushing the tyre away from the beading and sealing the white wall between the rim and the tyre (I'd recommend this), or you can cut some of the trim off, deflate the tyre and press it between the tyre and the rim. I did this and they keep slipping off.
Also, scrap your standard wheel weights on the steel wheels or they'll press against your white wall trim and make it stick out a bit (they have on mine). Alloy wheel weights which go on the inside of the rim would be perfect
Finally, you'll need some red rubber grease to put between the tyre and the trim or they'll wear the side of the tyre away! They're actually banned in some countries because of this...
As for the moon discs, also off Evilbay. Try a search for "full moon hubcaps", although there are several slightly different styles. They're a pain in the arse to be honest. They squeak like crazy constantly and every internet tip to stop this doesn't actually work. My solution was to put black gutter sealant behind the discs and this did the job, although it made them a nightmare to take off and they nearly bent!
It might also be worth mentioning that Fiat do a specific retro chrome hubcap for the 500 which will look great on yours. I couldn't get them for mine as they have the 500 emblem on so would look daft on a Panda. I'd go for these over any moon discs given all the hassle.
Also, if you don't fancy all the bother with the white wall trims (I'm getting rid!), check out
www.mrwhitewalls.com - If only hindsight came before you tried things
That said, they do look amazing and have got lots of comments.