As this is a very specific item I'd expect that there aren't any free plans for it online and possibly none at all; haven't looked though, but I presume you did already and came up short.
But if it helps it is quite similar in general outline to some clothes airers, just with vertical members where on an airer there would be horizontal dowel rods. If you can find plans for an airer of this type it could be easy enough to adapt.
I think you could reverse-engineer it just from the photo though, maybe making a prototype in pine first to iron out any kinks before committing to hardwood.