I just did this for my parents. If this scenario is appropriate, contact the small hometown paper where they were married. Get a copy of their engagement announcement from the archives of the paper to present to them along w/ a photo album of their lives together. To make it more special, try to sprinkle w/ copies of pics from outside your immediate family (i.e. aunts and uncles) so the pics will be items that they haven’t seen a bunch of times over the past 50 years. Or just focus on pics of when they were dating, newlyweds, etc. if you have enough.