jjesse,
It seems they Serial Number is accessible via a view.  The following from the "Computers by Serial Number" report:

SELECT DISTINCT     
    i.[Guid],
i.[Name],  
i.[Domain],      
s.[Identifying Number] [Serial Number]          
FROM dbo.vComputer i

JOIN dbo.vHWComputerSystem  s 
  ON s.[_ResourceGuid] = i.[Guid]      

JOIN dbo.CollectionMembership cm 
ON i.[Guid] = cm.ResourceGuid 
JOIN dbo.vCollection it 
ON it.Guid = cm.CollectionGuid 
WHERE s.[Identifying Number] <> 'Not Found'     
AND s.[Identifying Number] <> 'No Asset Tag'     
AND s.[Identifying Number] <> 'not yet supported'   
AND LOWER (s.[Identifying Number]) LIKE LOWER ('%Serial Number%')   
AND LOWER (i.[Name]) LIKE LOWER ('%ComputerName%')   
AND i.[Domain] LIKE '%Domain%'  
AND lower (it.[Guid]) LIKE lower ('%Filter%')   
ORDER By i.[Name]

Inv_HW_Computer_System

  .[Identifying Number].  There is also a [Serial Number] column in the Inv_HW_Baseboard table.

Clearly, alot of our custom reports are going to have to be re-written...or the legacy tables will need to be reconstructed as Views against the new Inventory schema (and frankly I'm surprised that they aren't already).

How about trying the Inv_HW_Chassis table?  There's also the "Identifying Number" column in Inv_HW_Computer_System.