Your best bet is to check on Craigslist, Trulia Rents, and with local property managers.
Put in a search on Trulia and you will be notified when something new that matches comes up.
It's very tough right now to find this type of rental in Marin. You might think about doing a house share. You can find opportunities on Craigslist and also by sending your needs to all your friends; and checking in the areas you like at the grocery stores, cafe's etc. on their bulletin boards.
Rentals used to be listed on MLS but not so much anymore, especially something small and reasonably priced. Get the word out everyway you can. Best of luck. Maryann