Use the standard round-robin that you can find by following the 'schedules' link near the top of this page and selecting 14 items. This will give you the first 13 rounds, another copy will take you to 26 rounds, then take the final 6 rounds from the top of a third copy. If you don't want to have the same opponents in the same order for each copy, then make a different assignment of the 14 teams to the numbers 1 to 14 for each copy.
