Bagteria is a My Poupette seller on eBay and she often has cadenas. I bought a palladium heart for me and a gold one for a gift in February and they were perfect. Her prices for cadenas are the most reasonable I've seen, also.
they had lots of them in the paris sale, so they could even re-appear next year, so if all else fails check ebay in late january but i could've sworn that i've seen them in boutiques fairly recently :s luxury-shops have a gold one but it's a bit expensive..
I haven't seen the heart in my boutique. I've purchased a couple of cadenas online. This is the first I have heard of fake cadenas...I can't believe those darned fraudsters! Does anyone know which have been faked? Argh....
Don't give up in the stores. They often have older ones on stock. I was searching for the 2006 sailboat to match my my bag with the same yearstamp and found it recently. And have a look online at hermes.com - I recognized that they not only have the ones from the actual theme.