These cute little goodies are available via ThinkGeek:
"We know you're flush with Mario goodies... but who can resist a squishy keychain to show off your Nintendo Fanboy (or girl) dedication? Since this is "New" Super Mario Brothers paraphernalia the coveted Mega Mushroom is included in the random assortment. But please don't let your dog chew on the power mushroom... lest he grow huge and start jumping on Goombas.
Please keep in mind that these New Super Mario Keychains are limited edition Japanese imported capsule toys and are random packed. When we sell out, these are gone and we cannot get more. You cannot choose the specific model you receive. Please read the sidebar below for more information."
Found via geek24.com.