Im making a strawberry tart where the sauce is made from boiling thyme, port/tawny and strawberry juice. Is there any replacement for thyme in this?
The flavour of thyme can't be imitated by substitution. You can either omit it or devise a different sauce. Various herbs (basil for example) are combined with strawberries in various dishes, but the proportions are up to you. You may want to search for recipes using both strawberries and each of the available herbs to help with both selection and quantity.