Some one mentioned in another thread of shops on esty that could do adult onesies.
Just received my order from Nora made me, for a sleeveless onesie... also a received a normal onesie, both are fantastic, they look great, are very comfortable to wear which allows me to wear out more. Pretty reasonable pricing aswell, and she does her best to make them to your size with the measurements you provide. Also great for me as she is NZ local so for once I get to save on shipping. YAY! She also has a deal to appeal more to the overseas crowd by 4 get 1 free.
But absolutely love what I received.
Wearing the sleeveless one right now