Have you searched ITG and Pipercross? They both make a range of high flow foam filters used in race applications.
If you want the velocity stacks visible for aesthetics it restricts one to using the mesh style cap filters with limited functionality, however the Chinese design shown above using a foam sandwich which is the diameter of the top of the velocity stack will likely be too restrictive in flow. The alternative is to cover the stacks with either single filters that the stacks sit inside or as a group. Making a Lexan top to see them is then a lot easier.
