If you're importing profiles into your nation, you can import a column for the field "signup_type" to indicate whether the profile is a person (denoted by a 0) or an organization (denoted by a 1). This process is described in more detail on this FAQ. 

If you're concerned about organization profiles that are being imported via Twitter, you can add the profiles you've identified as organizations to a list, and batch update their "Type" to "Organization."