To be precise: One out of two manufacturers. Pacific cycles is the manufacturer of all birdy-frames, but who is the manufacturer of the bike depends on where you live. Pacific-Cycles covers more or less all of Asia, Riese and Müller (the original inventor) covers Europe and probably the rest of the world. Their site is here:

https://www.r-m.de/en-gb/

Not sure where you are living and also not sure who is the manufacturer of the Birdys that are/were sold in the US.
R-M do still provide a manual for the old model of the Birdy up to 2006, unfortunately only the German version (at least I did only find this one):

https://www.r-m.de/media/filer_publi...2d/ba_b_04.pdf

On page 54 are the torque-numbers, on page 55 the guide for inspection, so this may still be helpful. Or you could send them an email and ask if they have an english version available.

Over the years there have been a lot of changes on the Birdy, here's a German page that provides a changelog (in German) birdy-freunde - Modellpflege beim Birdy as well as a load of older documents, catalogues and manuals: birdy-freunde - Dokumentationen