Check out this post by Mary Corbet on the NeedlenThread forum.
I known Mark Harris personally for over a couple of years when he moved with his wife to Canada from Australia and he came around and showed me his beautifully made slate frames.
They have now moved to England and are setting up his workshop there. He is taking pre-orders for slate frames and trestles at a good price, so he can purchase the equipment to make the frames and trestles in England.
I would highly recommend Marks frames and stands.
It may take a while for you to get the slate frame or trestles as he will be busy for a while setting up and making the pre-orders, but it will be well worth the wait.