select tt.tovar_id,sum(tt.count1) as [Количество_таблиц_с_товаром]
from
(
select 1 as count1, tovar_id as tovar_id from T1 group by tovar_id
union all
select 1 as count1, tovar_id as tovar_id from T2 group by tovar_id
union all
select 1 as count1, tovar_id as tovar_id from T3 group by tovar_id
union all
select 1 as count1, tovar_id as tovar_id from T4 group by tovar_id
union all
select 1 as count1, tovar_id as tovar_id from T5 group by tovar_id
union all
select 1 as count1, tovar_id as tovar_id from T6 group by tovar_id
union all
select 1 as count1, tovar_id as tovar_id from T7 group by tovar_id
union all
select 1 as count1, tovar_id as tovar_id from T8 group by tovar_id
union all
select 1 as count1, tovar_id as tovar_id from T9 group by tovar_id
union all
select 1 as count1, tovar_id as tovar_id from T10 group by tovar_id
union all
select 1 as count1, tovar_id as tovar_id from T11 group by tovar_id
union all
select 1 as count1, tovar_id as tovar_id from T12 group by tovar_id
) tt group by tt.tovar_id
-- или так
--having count(*)>=3
-- и так тоже кошерно
having sum(tt.count1)>=3

With All_Tables as
(
select 'T1'  as TableName, tovar_id, tovar_name from T1
union all
select 'T2'  as TableName, tovar_id, tovar_name from T2
union all
select 'T3'  as TableName, tovar_id, tovar_name from T3
union all
select 'T4'  as TableName, tovar_id, tovar_name from T4
union all
select 'T5'  as TableName, tovar_id, tovar_name from T5
union all
select 'T6'  as TableName, tovar_id, tovar_name from T6
union all
select 'T7'  as TableName, tovar_id, tovar_name from T7
union all
select 'T8'  as TableName, tovar_id, tovar_name from T8
union all
select 'T9'  as TableName, tovar_id, tovar_name from T9
union all
select 'T10' as TableName, tovar_id, tovar_name from T10
union all
select 'T11' as TableName, tovar_id, tovar_name from T11
union all
select 'T12' as TableName, tovar_id, tovar_name from T12
)
Select tovar_id, tovar_name,
 stuff((Select distinct ', '+ TableName From All_Tables b Where a.tovar_id = b.tovar_id and a.tovar_name = b.tovar_name For XML path('')),1,2,'')
 From All_Tables a
Group by a.tovar_id, a.tovar_name
Having count(distinct TableName)>=3