Tony built his flow hood over 5 years ago with the assistance of a builder. At this time we do not offer any services to help to build your own flow hood. You can also check out our blog for some other suggestions.
The 12 x 24 filter that we used on our DIY laminar flow hood video is from a company called AAF Flanders.
Myers Mushrooms also has some filters for purchase. This company has pre-assembled hoods.
We recommend joining our Mushroom Growers group on Facebook, where we have many growers who have built their own flow hoods and may be able to assist you further. Another great place for mushroom growing help, if you don't use Facebook, is Mushroom Growers on Reddit.