There was the notorious Fluttershy one on ebay which seemed to keep being bid up to thousands of dollars and although that was obviously ebay trolls it was very cute.
I dont think [or at least I havent seen anyone claim to spot one] its a product which has been licensed - with the exception of sites like welovefine, MLP licensing is still largely for children's products.
Depending on quality, finish, size and type of material you can easily get one made - they can become a little pricey if its completely bespoke. But I have had several made for client promotional/experiential stands over the years...as a starting point just Google something like "custom welcome mats" or "bespoke welcome mats"