Eminent Technology ET-2 Air Filter

Motor Guard D-12-2 is what I use.  They're much more substantial than the factory filter as they remove moisture, too.  The thread is 1/4" npt, so you'll just need to get some barbs from a hardware store to adapt it to your tubing.
https://www.amazon.com/Motor-Guard-D-12-2-Disposable-Filter/dp/B000KSTEZO

Thanks so much - just placed my order!

Personally, I'd rather had a clear housing so as to see inside.

There's no reason at all to see inside the filter.  It won't do anything for you.  A loss of pressure will indicate that it's time to change the filter.  If you don't have a gauge after the filter, you really should think about getting one.  If you don't want one for some reason, the filters are cheap enough to replace annually or whenever depending on how often the pump runs.  Installing a gauge and only replacing filters when pressure drops is most likely the more cost effective option, though, since they only cost a couple bucks.