Many early modern and later buttons were made of metal and are therefore often found by metal detectors. The database of the Portable Antiquities Scheme is a good resource for information on these types of button. If looking for examples of early modern buttons go to the advanced search option at http://finds.org.uk/database/search/advanced . Under main details chose object type - button, and under temporal details chose broad period - Post Medieval, and sub period - early, this will give you mainly 16th and 17th century buttons. The result will be around 300 examples of period buttons. Click on a find number for full details, this should give you a photograph and a complete description. The photo below, though of a mid 17th century button is not from the database.