I found a thread from a year ago concerning an adult sized Bjorn Bouncy or Balance chair. The thread is now closed, otherwise I would have posted there. The post included the following link with a picture:
Look! Baby Bouncer For Adults | Apartment Therapy
I decided to write to the company and ask them if these adult sized chairs were available for sale. The replied promptly and this is what they said:
Thank you for contacting BabySwede. I am sorry the bouncers at the expo where for demonstration only. BabyBjörn currently does not sell the Babysitter balance in the adult version. I will pass your suggestion onto our product development team. We thank you for your interest in BabyBjörn!
Danielle M. Falvy
Baby carrier, bouncer, high chair
I am thinking that if enough people write to them requesting this chair, perhaps they would consider making these chairs available.