Best wishes and prayers for your Dad and all the family. As you did not mention his age, or the ages of the children, I would also like to suggest that you let his need be known to his friends, co-workers, neighbors, club members, church/synagogue members, etc., so as to have a larger pool of possible donors to look over. In addition to the matching and general health tests, some people may be better able to donate than others due to better insurance coverage, greater facility to miss work, fewer family oblications, etc.
Fr. Pat