No, it isn't common for farmhouses that offer accommodation to offer work on their websites - but it doesn't mean they wouldn't be open to the idea. Look for estates that grow olives, grapes or other agricultural products and contact them directly, it will be the only way to find out.
On an organized side, there is WWOOF -
http://www.wwoof.it/en/ - an organzied way to bring together thsoe who want to volunteer on small organic farms in exchange for the experience. So you can look into that as well as a possibility.
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