How can I find Robert Hunter and/or Justin Hunter?

I'm looking for Robert who is approx. 51 and Justin who is 31. I know Robert was in Cheyenne, WY in July and/or August of 1983, which is when and where Justin was born. I believe Robert's wife's name, at the time, was Leslie. I believe he remarried, at least once. His second wife's name was possibly Sarah. I also have reason to believe Robert's family originally immigrated from Scotland in the early 1900s. Robert is my biological father; Justin, half brother. I've never met them. I'm not really sure what I'm going to do if I ever find them, but I don't want to regret never looking.