Open marriage as in you can have sex with anyone you want or open marriage as in you are going to have other actual romantic relationships with others?
If the first one... You can continue to use your swinging resources... SLS or other websites, parties, etc. Some dating sites can also be used to look for hookups. I know OKCupid has casual sex as an option in the "what you're looking for" area. Since you're doing it more one-on-one, if your area has an active bar scene you could try that route, but that idea has always made me a little nervous.
If the second... I have had luck on OKCupid meeting people that I've become friends with (no relationship has sprung from it, but there are some awesome people), other online resources (there are poly websites and a few other dating sites that are open relationship friendly), normal everyday life (my first boyfriend after opening up to poly was a guy I met in class), swinging situations with the right people (met current girlfriend this way)