So ... are you still looking?
This is the first one I posted and it looks to be what you need:
The others you posted, could be home made or assembled, however, the long slot would be difficult to make without a milling machine, unless it was made of brass.The easels do look home made so that may be the case.
They could be made from wood, but they would need to be much thicker for strength. There's another concept for adjusting to given angles that uses legs that nest in a series on step or notches inside the case that could be made from thinner wood.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
Last edited by woodnthings; 06-25-2019 at 10:29 AM.