Guf,

Делал аналогичную задачу.
В отдельную таблицу занес по контрагентам все нерабочие дни, включая сб и вс, т.к. бывает что и выходные рабочие по всяким праздникам.
Потом процедуру нарисовал отдачи календаря по каждому контрагенту.
CREATE TABLE [dbo].[market_no_work_date](
[mkt_id] [dbo].[refer] NOT NULL,
[no_work_date] [date] NOT NULL)


Create proc [dbo].[get_market_work_day]
(
@mkt_id refer
,@DateFrom date=null
,@DateTo date=null
)
as
Begin
Select @DateFrom=isnull(@DateFrom,getdate())
Select @DateTo=isnull(@DateTo,getdate())
;WITH
L0 AS (SELECT 0 AS c UNION ALL SELECT 0),
L1 AS (SELECT 0 AS c FROM L0 AS A CROSS JOIN L0 AS B),
L2 AS (SELECT 0 AS c FROM L1 AS A CROSS JOIN L1 AS B),
L3 AS (SELECT 0 AS c FROM L2 AS A CROSS JOIN L2 AS B),
L4 AS (SELECT 0 AS c FROM L3 AS A CROSS JOIN L3 AS B),
Nums AS (SELECT ROW_NUMBER() OVER(ORDER BY (SELECT 0)) AS n FROM L4)
,dates as (SELECT cast(dateadd(dd,n-1,@DateFrom) as date) d FROM Nums)
,dates_row as (Select ROW_NUMBER() OVER(PARTITION BY mnwd.no_work_date ORDER BY mnwd.no_work_date) AS RowN,d.d,mnwd.no_work_date From dates d
left outer join market_no_work_date mnwd on d.d=mnwd.no_work_date and mnwd.mkt_id=@mkt_id)
Select d,case when no_work_date is null then 1 else 0 end as work_day from dates_row
Where d<=@DateTo
End