I've trawled through all the early newsletters and this is the only image I have been able to find. It was taken at the Beaulieu Classic Boat Festival of June 1997 and refers to the JRA stand at that event. The reporter was Robin Blain.
Not a very clear photo but enough to show the size and proportions.
JRA Newsletter issue 34 April 1999 page 7
On further study of the photo (enlarged a bit) it looks as though there are two of them: the tan sail on the left and a white junk sail centre, partly behind the man in the middle of the photo. Both model rigs look to be considerably taller than 60cm.
The caption refers to "3 working model rigs that were borrowed from Sunbird Marine..." - so I guess that thing on the right is also some kind of working model.
Maybe that will jog some memories.
The newsletter article (Issue 34) also states that "Sunbirds have built and supplied a model junk rig for Bruce Roberts in the USA so members going to boatshows in the States should see it on display".
The only other reference I could find to a model junk rig is in Issue 30 (July 1995) where there is an article by Robert Bolton with photos of a RC controlled model junk with a Reddish rig. This model is not attributed to Robin Blain though it is the subject of a letter written to him.