top filter for the 800D.DEMCiflex makes one i've seen it on the net.
http://www.demcifilter.com/contact.php
We do filter sets for Antec 900,1100,1200, Cooler Master HAF X, 932,922,912,CM Enforcer, CM Storm Trooper, CM 690 AdvII, Corsair 600T,650D, 800D, 400R, 500R NZXT Phantom, NZXT Phantom 410, Zalman Z9, Silverstone,
If you scroll down to bottom of page this site sells them.
I have no idea where this shop is but it proves the filter you seek exist.
http://jerryrandomitshop.weebly.com/demciflex-filter.html
Just go through DEMCiflex or contact someone like http://www.frozencpu.com/cat/l3/g47/c223/s1024/list/p1/Fan_Accessories-Fan_Filters-DEMCi_Flex_Fan_Filters-Page1.html
DEMCiflex Triple 120mm Magnetic Dust / Fan Filter
http://www.frozencpu.com/products/11724/ffi-52/DEMCiflex_Triple_120mm_Magnetic_Dust_Fan_Filter_-_Triple_Radiator_or_Fans_-_Steel_Aluminum_Plastic_Chassis.html?tl=g47c223s1024