In fact, having re-read your posting:
The issue here, I surmise, is that you backed out of the rental agreement before you moved in, and you are depending on the landlord to re-rent for you to cover the term of the lease. You are actively seeking a replacement tenant yourself, and you depend on the landlord's cooperation to make this work, and he seems not to be cooperating.
I would send a letter, certified, etc. reviewing the circumstances, that you have found potential tenants but you have found yourself frustrated in showing the apartment due to the landlord's lack of cooperation.
Point out that he has an obligation to mitigate his damages by renting out the apartment, and that obviously no replacement tenant will be found without his cooperation to show the apartment, and to finalize any deal. By his refusal to cooperate, he must surely realize that he is taking on the responsibility to limit your liability under the lease, if not to release you completely.
Give him the names and telephone numbers of the tenants that you want to show to, ask him to call and arrange to show them, and give him a schedule when you will be available to show the unit yourself, if he prefers. Also invite him to give a schedule of his own, if yours is not convenient. Require that he answer and give him a time limit.
Keep in touch with the listed tenants to see if he ever really contacted them. You may need them in court.