1. Find a phone number and call the cemetery.
Good morning/afternoon. I am calling on behalf of Democrats Abroad and we would like to participate in your Memorial Day ceremony and lay a wreath to honor those who made the ultimate sacrifice... Would that be possible? It would be such an honor and privilege for us. Who is in charge of the ceremony? Who is your florist? Do we need a car pass?
2. Order a wreath. Ideas for a wreath include red, white and blue flowers in the shape of the American flag. You can also ask for a blue ribbon with Democrats Abroad on it and possibly "Lest we forget"
3. Follow up with the cemetery and florist by email.
If the location is governed by the American Battle Monuments Commission (ABMC), there will be a Superintendent who is a US Federal employee and responsible for all such events. Direct contact with this person (or an immediate subordinate) is the best way to make any arrangements.
It would not be unusual for the official ceremony to take place on the Saturday or Sunday of the weekend. In that case, there will be a strict protocol for when and where to drop off the wreath (usually hours before the ceremony), the role you play in the ceremony, and how many people may directly participate.
If there is no official ceremony that day, the Superintendent will usually be very happy to host a small party, even give a tour, and that person will also tell you what kind of wreath would be appropriate and where to put it. Photos are not only allowed but encouraged, but a full photo-shoot with reflectors and tripods would require special permission.
As far as timing, the earlier the better.
American Battle Monuments Commission (ABMC) https://www.abmc.gov/
Commonwealth War Graves Commission (CWGC) https://www.cwgc.org/