Great idea! It's such a fascinating subject. Like, you'd think there'd be more, but when you actually look at it, there's very little. The strangest thing is that beanie from like, 2005. That was after The Muppets were sold to Disney, so it's very mysterious (to the point where I'm almost wondering if it was sold without Disney's approval.)
There is more than that. I was actually looking at the rather horrifying Sesame Street Halloween costumes made by Ben Copper and apparently there was a kermit costume made. I'm a bit iffy thought because it looks like the Baby Kermit costume and might just be a factory error
I used to think Kermit didn't appear in much Sesame Street merchandise because I used to think that both Henson and Sesame Workshop co-owned the Sesame Street characters until 2000 and maybe Henson didn't want their fully owned character in Sesame Workshop merchandise. But I think it might be more a branding thing, with one company being able to release Sesame Street merchandise and others being allowed to release The Muppets/The Muppet Show merchandise and it'd make more sense for Kermit to be part of the Muppets merchandise, and sometimes the same companies would license both Muppet and Sesame Street merchandise (but I think they still wouldn't be allowed to freely use characters from different properties as part of the same collection).
Though Sesame Street began seven years before The Muppet Show, and there wasn't much official merchandise with Kermit included before that (though the first Kermit toy was released before Sesame Street premiered). That could have been plenty of time to include Kermit in more Sesame merchandise, unless Henson was already preparing for him to be part of The Muppet Show (likely), or in case one of the pre-TMS specials got some merchandise.
Here is one interesting appearance. The Silly Storytime DVD. I think it's really cool that they made a whole new reporter Kermit photo puppet just for the cover of this DVD. This was after Disney bought the Muppets so he's listed as a special guest but that's still pretty cool