First, you need to compile a proposal of your reality show idea. Cover all details, such as what sort of a reality show you have planned, how many participants are going to take part in the show and what will be the prize for the winning participant.
In a second proposal, specify the minor details such as the location at which the show is going to be hosted, episode structure, any necessary arrangements for housing facilities etc.
Next, you need to contact a television network that films reality shows and is willing to take a look at your proposal. You can use the internet for this purpose. Search for a list of TV networks that are currently doing a reality TV show or plan to do one in the near future.
Contact as many networks as you can and tell them about your reality show idea. Be as comprehensive as possible in the initial conversation and only give details those are absolutely necessary. If a network shows interest in your idea, you can then go ahead and send them the proposal.
Do not be afraid to get rejected because a reality show idea is something that has to be unique and attractive if it is to be filmed. Wait for the first network to get back to you with a final answer. In case of a rejection, try another television network. But before you do that, remember to go through the script of your reality show proposal and see if you can make any improvements to it.