Michel,
Short answer: Not available.
Long answer, read on:
The 'square' Douglas kneegrips were an option on the 350cc and 600EW, but likely could be had with any of the other models. Yes, the same 'grip has been seen on the RA model. They applied for a British patent covering the frame mounted bracket on September 23, 1926 (GB273,937).
They also applied for Registered Design protection on the bracket. As typical practice of the time, they crossed out on the photograph the portions of the image that did not apply to the registration.
However, in a close up view (photo of a photo!), one can see that wee-Jamie is of uniform thickness with some level of incised detail. That is, not a full bass-relief carving.
I did get a photo of a survivor c1988 that showed a hint of the detail on wee-Jamie.
Facial details, vest, sporran, and socks can just be seen. Unfortunately this was the best view that could be had at the time as the photographer's better camera and equipment were destroyed in accidental house fire! Pestering for a redo did not seem tactful at the time. The plan had been to make a pattern and mold new kneegips.
A fossilized example was borrowed and that yielded the basic design of the structure and shape; some estimation for shrinkage and distortion required.
But as far as detail went, only the diamond pattern in the socks could be discerned.
Fast forward to 2010 and another opportunity came up for images of the kneegrip last photographed in 1988. In the intervening twenty-two years, any residual detail had weathered away. Only the diamond pattern on the socks was still apparent. It must have been the detail carved the deepest.
To that end I had an artist friend (that owed me for a welding favor!) prepare a few concept sketches of varying levels of detail for wee-Jamie, but I never settled on one design nor found the time to tackle the project properly.
-Doug