Today we got several reports of a Grubber Plush being spotted on Ebay. Not else was known at the moment like a manufacturer. I decided to do some research and found out there's a very high change he was made by Bandai Namco.
What's very interesting is that besides Grubber, there's apparently a Capper Plush as well and he looks adorable! But of course some of the main cast can't be left behind as well as there's also a Seapony Rainbow Dash and Twilight Sparkle. We also see Tempest Shadow who we first thought was actually made by Play-by-Play. However there's still a change that perhaps Bandai Licensed these plush from Play by Play as the regular Mane-Six Plush (which can been seen on their website) shares some similarities with their plush from several years ago.

On their website they sell a lot of arcade-like items like arcade games but also prize items like these plush. So it's very likely you can find these in several claw-machines. Some people already reported finding them inside claw-machines. Perhaps it's time to check out some of your local arcades or fun fairs as well? Let us know if you find any of them!