Virginia is a state that mandates that swans be euthanized or not treated because they deem them as a invasive species, which they are not and you can see what is happening in New York (Regal Swan Foundation Facebook) with this same issue. So, even if there had not been something wrong with your swan, they may still have killed it. We are fighting this wrongful atrocity in several states.

In any case, the chances that Virginia will allow you to introduce another Mute Swan is questionable at best. We would suggest that you check around to see if you first, can find a mate and then you need to determine the age of the male.

Not all males will re-pair, so he may be just as happy alone then trying to introduce another mate, which he may or may not accept.

In order to introduce another swan, you will need to build a pen (enclosed totally top to bottom) so that no predators can climb into or dig under. Place a feeder in the pen, with the pen having a zero entrance. The pen needs to be 1/2 on land and 1/2 in water. You will need to keep the new swan in the pen for approximately 2 weeks to acclimate her to you, the feeding system, the habitat and the male. If there are any signs of aggression, then you cannot release her. Once you release her, keep a boat/kayak readily accessible so that in the event of an emergency rescue, you can capture her and find her a new home. Again, this may be difficult with your state laws regarding swans and where you may or may not be able to relocate her. The Regal Swan