You could still join until a couple of years ago and get advice from members in the clinic section, but they have even closed that now.
Bart (the founder of the site) was very helpful. I saw him post on another forum I think but not recently.
There was a member, Disburden, who is super knowledgeable and skillful - he helped me out a couple of times and his advice was on point. He sometimes crops up.
Gary Haywood is British. He is seen honing in some of the videos and respected as one of the best coticule honers in the world judging by the comments I've read about him. I bought a coticule from him. He was so helpful - giving me a load of advice by email. If you ever come across him, really worth picking his brains.
There is little good advice on coticule use these days, but if you dig back into the archives of older forums you can find quite a bit.
I also think that Ardennes coticules did themselves no favours. They created a lot of hype about Veinette stones and then that was all anyone was interested in. Then they stopped listing the layers they were selling.
It seemed to kill the interest in coticules. I know one seller who stopped selling coticules altogether because it became too difficult working with customers to get the precise stone they wanted.