Airlines should be forced to purchase new spare parts from the manufacturer. If they cannot afford genuine parts, then perhaps they shouldn't be flying at all. I guess there are some parts that do not affect the airworthiness of an aircraft, such as toilet seats, toilet paper dispensers etc, which is why each and every manufacturer should specify which parts must be purchased new, and which parts can be bought from third party sources.
I do realise, however, that operators of L1011's and other old equipment, may have to rely on second hand parts.