When you can't get house parts, try auto and computer parts.

Get some 120mm fans (or an array of 80mm, etc), and some engine air filters.

Don't change the filters too often:

"It is common, however, for servicing to occur when the filter appears dirty. Engine air filters are designed to actually increase their efficiency by using this initial layer of dust as an added filter layer. Initial filter efficiency is usually approximately 98% but increases to more than 99% by the end of the service life of the filter.

Therefore, changing an air filter before the useful service life is achieved can result in premature engine wear."

https://www.fueleconomy.gov/feg/pdfs/Air_Filter_Effects_02_2...