Robert White is a family owned photographic supplier that my friend Richard told me about. Although they supply the standard camera gear that all suppliers do, they also supply some of the more unusual hard to get hold of stuff in th UK. There prices are usually competitive too.
What I also like about them is they produce many videos that show you some of this stuff.
Below is a video they posted a few days ago and some of the images within it are breathtaking:
I must admit that I am toying with the idea of purcashing a Lee Filter split-grad kit and this is the first place I’ll go.