If you get no joy finding a courier it might be worth your while phoning the RPRA (01452 713529) and ask them if they could put you in contact with a local fancier who could collect and house the pigeon till you get a courier sorted.
http://www.distancesfrom.com/gb/Kincardine-Bridge-latitude-longitude-Kincardine-Bridge-latitude-Kincardine-Bridge-longitude/LatLongHistory/7577631.aspx The Latitude of Wallacestone is 55.9769. The Longitude of Wallacestone is -3.7341. The Latitude of Kincardine Bridge is 56.0643. The Longitude of Kincardine Bridge is -3.73. .
Canker but I have seen pigeon pox inside a pigeons throat that looks similar but this is normally accompanied with pox on the outside of the beak and eyes ceres.