I replaced mine just after i got my car, so I didn't really know about a lot of the parts websites yet. I got mine on Ebay.. the rear one I got from
this guy who doesn't seem to have any rear ones listed at this particular moment.. I was lucky enough to get my back emblem (the blue one) from someone for a grand total of $5.99, though.
How to replace them depends.. The front one should pretty much just require prising the old one off carefully, removing all the adhesive stuff that's left behind, and applying the new one. Mine came with the stuff to adhere it right in the package.
My rear one is the kind that swings around to reveal the trunk latch, so it's more complicated to replace.. 05YellowBeetle.. yours shouldn't be that kind, so I don't know if the process would be similar to the front or not.
Here's a How-To:
http://newbeetle.org/vb3/showthread.php?p=942