Box to stretch abductors

Hi, I’m 48 and have cerebral palsy.
Over 20 years ago I had a box that I sat on to stretch my abductors. My mum got rid of the box when I moved into my own place! Now, I’m trying to find the same type of box and wonder if someone could advise me where i could get one.

The thing I had was a rectangular wooden box with a rounded (and padded) top. Back in the day, physios referred to it as a ‘horse’. Now, people either don’t know what I mean or don’t know where I could get one.

Do you know what I mean/know where I could get one?

If you have such a box, please could you give me the measurements of it so I can have one made?

Thank you
Patrick