Hello Joey,

Please see User Guide ( www.ti.com/tool/TIDA-00378 ), page 20.  The enclosure is made by Sharp:

5.2 Sensor Assembly 

The PM2.5/PM10 Particle Sensor AFE Design is designed to attach directly to the optical chamber of the Sharp Microelectronics optical dust sensor (part number: GP2Y1010AU0F).

I see DigiKey carries these, although none in stock right now: www.digikey.com/product-detail/en/sharp-microelectronics/GP2Y1010AU0F/425-2068-ND/720164   

~Leonard