AilsI believe they used to be available in Amazon or eBay. It's probably worth checking out.
Oh and they're available through GeekKeys aswell.
Here's a link for the White set:
http://www.geekkeys.com/vortex-white-backlit-thick-pbt-108-keyset/
(they have them in more color options besides White and Black too)
AilsThey're on mechanicalkeyboards.com...but out of stock. :/
I can't imagine it'll be too long before there's another drop here--there's already 800 requests since the last drop ended.
If you can't wait, ducky has a set of POM double-shot caps with translucent legends. Don't know how they compare quality-wise, but I've heard good things about ducky. https://mechanicalkeyboards.com/shop/index.php?l=product_detail&p=1579