I go to Subway, smile, and ask them if I can have some olive oil packets for camping. They usually ask "How many?" , and I end up with quite a handful. Never been denied.
Also, look for "single serving" salad dressing packets at supermarket salad bars. Newman's Italian is great. (not Creamy Italian.)
If you need a large quantity, try minimus.biz, but only if you can put together an order large enough to justify shipping.
Edit: Corrected typo. Thanks Bob.