Fans and blowers are specified using a number of parameters, including electrical (voltage/current), size (diameter/thickness/mounting configuration), and process (flow rate and static pressure). Here is a sample Digi-Key search string, sorted descending by flow rate, filtered to only show fans rated for 50-200 CFM at 24 VDC and under 60 dB ambient noise. As Jake discusses in his PPH-PPE project, better fan datasheets actually show a flow curve that relates maximum flow rate to pressure drop, such as this one from Orion:
The fan will need to pull air from the box and through a suitable filter which will add some non-zero pressure drop to the system; 1 inH2O is a reasonable starting point based on this document from the EPA on HEPA filters. So the simulation should ideally give us two numbers: a flow rate and an overall setup pressure drop, which we can then use for fan sizing and selection.