Difficult Query: Can Only Modify The WHERE Clause
Count the number of rows for every distribution and compare that to the number of rows returned for a distribution where you apply your filter.

declare @T table
(
  Distributor char(3),
  Reseller varchar(10),
  State char(2)
);

insert into @T values
('ABC', 'BestBuy',    'CA'),
('ABC', 'RadioShack', 'NJ'),
('XYZ', 'BestBuy',    'CA'),
('XYZ', 'RadioShack', 'MO');

select T1.Distributor
from @T as T1
where (
      select count(*)
      from @T as T2
      where T1.Distributor =T2.Distributor
      ) = 
      (
      select count(*)
      from @T as T3
      where T1.Distributor =T3.Distributor and  
            (
            T3.Reseller = 'BestBuy' and T3.State='CA' or 
            T3.Reseller = 'RadioShack' and T3.State='NJ'
            )
      );

select T1.Distributor
from @T as T1
where (
      select count(*)
      from @T as T2
      where T1.Distributor =T2.Distributor
      ) = 
      (
      select count(*)
      from @T as T3
      where T1.Distributor =T3.Distributor and  
            (
            T3.Reseller = 'BestBuy' and T3.State='MO' or 
            T3.Reseller = 'RadioShack' and T3.State='NJ'
            )
      );