Unfortunately, it's so easy to print whatever the heck you want on a t shirt or a cup or sticker, so there's plenty of cheap C&H merchandise out there.
For me, knowing they are unsanctioned keeps the memories of reading calvin and hobbes completely pure: this isn't them as they were intended to be, but bastardized facsimiles for the purpose commercial gain. It's somewhat poignant; there were many a C&H comic concerning the evils of advertising and marketing - to see subject to it as well completes the message quit succinctly.