The RSPB: Bird guide: Red, amber and green explained
www.rspb.org.uk
Birds of Conservation Concern 4: the Red List for Birds | BTO - British ...
https://www.bto.org/science/monitoring/psob
I do not recall the year, number and edition, but several year ago National Geographic did a number dedicated to the endemism of birds around the world.
And last but not least, check the website for the of the Smithsonian Institute
The classic checklist of birds of the world of Howard & Moore can be useful, and also the one published by Clements. There are different editions of both.
You are probably right, Indonesia (419), Australia (317), and may be Brazil (233) are possibly the countries with the highest number of endemic birds these days
However, you should check birdlife international website, and look for country profiles:
http://www.birdlife.org/datazone/country
And also thess publications:
Orme, C. D. L., Davies, R. G., Burgess, M., Eigenbrod, F., Pickup, N., Olson, V. A., ... & Stattersfield, A. J. (2005). Global hotspots of species richness are not congruent with endemism or threat. Nature, 436(7053), 1016-1019.
Kier, G., Kreft, H., Lee, T. M., Jetz, W., Ibisch, P. L., Nowicki, C., ... & Barthlott, W. (2009). A global assessment of endemism and species richness across island and mainland regions. Proceedings of the National Academy of Sciences, 106(23), 9322-9327.