I can provide a slection of information regarding your problem. None of it is going to answer your qustion though, I am afraid.
It is porbably worth pointing out that the Outerwears are sort of a bandaid solution to keeping large particles (realtively speaking) of debris out of the filters in addition to providing a small measure of protection against liquids. With that said, everyone in the motorcycle/ATV world that run their vehicles without an airbox uses Outerwears (as do many other folks). The material that Outerwears are made of is actually used as a liquid straining (filtering) material in the food processing industry. With that said there are several places to buy the material in bulk, rather inexpensively. My company has been known to use this material to make our own pre-filters from time to time for a selection of applications. However, I cannot remember the excat place where we were getting the material from. I know the place is in or around Riverside, CA. I think the name might be Ironman or something like that. I remember the place a weirdo name. Anyways, they are a huge industrial filter supplier.
Once you get the material you will then have a problem "sewing" it. You have to heavily over-sew all the seems after thay have been heat sealed inorder to get a good, resilient part.
Moving right along, as you probably already know, given the option of making a solid shield for the air filter, that doesn't restrict air flow is the best thing you can do. Many times this isn't very feasible from a space claim perspective or the environment the filter is used in will compromise any efforts to shield the filter.
Like I said before, I'm porbably not the most helpful, but atleast I can relate to the headache this project will give you. Good luck! :thumbsup: