I can highly recommend this book to give insight into how people like Kelson sourced their rare specimens.Interestingly it would appear that one of the reasons Kelson travelled to Paris was that the 'Plume Trade' was outlawed in London during his time and supplies probably started to dry up.
For those interested ..a fascinating article on the defence offered by the feather trade..https://archive.org/stream/feathersfactsrep00royarich/feathersfactsrep00royarich_djvu.txt