Some television networks make use of short films by playing them during certain short timed blocks. You could therefore send a copy of the short film on DVD along with a cover letter to some networks’ short film acquisition executive.
You could also check your local video/DVD dealer to see if they would be interested in selling or renting out you kind of film. Having them view a sample of your films would definitely be a plus. If your film has documentary works or is based on a particular theme, you could look into advertising it to museums and universities, which tend to buy films of this nature from time to time.
Another popular way for you to market your short film is through the internet as many sites are available which will give you the opportunity to broadcast your film. Some are even designed, so as to allow you to generate some amount cast. Most of these however, only act as a means of giving you some amount of exposure. It’s all about marketing, not so much about creating. After your short film is in the can, focus all your energies on selling the product; the creative part is done.