You can get the uni filter ones from Kaizen most of the time. Ebay has them too. I got no idea about the others. Just try repco and look through all the books from speco thomas etc and you might get lucky. I guess you could try a carb tuning place if theres anywhere still around. Theyd know for sure. You see most carbs with filters like those. I dunno about those invisible ones, they may give a better airflow down the stack, but the filter area is greatly reduced over a normal uni filter. Theyd need more frequent cleaning and would need to be pretty free breathing to work effectively. Cheers Niz.