Lentil, are you saying that because the weddings are being held in barns that you're looking for a farm theme? And, if so, what sort of farming is most prevalent in the area? That, alone, should provide some clues.
For instance, if I were doing such down here I would decorate with old-style tobacco farming tools: Tobacco baskets, and chopping knives, and spikes, and tobacco sticks, etc. Maybe use a pair of tobacco setters to support tabletops. That sort of thing.
I'm guessing that where you are dairy is the big thing. If that's the case, old-fashioned milk cans, and three-legged spoons, and milking pails would work. Dairy cows are belled, and those would work as props, too.
I know there are miniature, decorative milk cans available. You could use them as centerpiece elements. Lot's of gingham, as it always says "farming." Maybe do the tablecloths out of it?
Canning jars are a great element for a farm theme. Use them decoratively, and for service (drinks, condiments, soups, salads, some apps and desserts can be served right in them). The larger (i.e. half-gallon) can also be used to hold floral displays and as elements in the centerpieces.