The way I`ve heard it told is by simply asking. I know that sounds too easy but that`s how it works. To be a little more specific when asking for rights I would ask for certain rights, such as, mail order rights, rights for a country (USA), etc. Provided a company is not currently marketing their product say for instance in mail order catalogs this would be a perfect opportunity for someone with mail order savvy. Now, when asking you`d better have your ducks in a row so to speak, meaning you need to convence the manufacturer, importer, etc that you have expertise in this area.
To kinda imagine how easy this would be to get these rights is put yourself in their shoes. Say you have a product and are not currently marketing it in the field that is requested, wouldn`t you be interested in listening to someone about helping you? You bet you would. So, again my advice to you is to, "get your ducks in a row" and go ahead and ask.
"How To" business start-up videos at www.qualityplusco.com