Mine got cracks. I paid about €200, maybe €260 to import a secondhand one from Japan. I got the tip that it was available, by posting a request on Birdy Global Community on Facebook. There is a guy there right now who says he is buying a Mk3 rear end and front forks on Ebay. The parts are manufactured in Taiwan and Pacific Cycles do not sell them separately. Another person in BGC said try Taobao website where there are some parts [it is in Chinese, do not know if they ship overseas but probably] .
The Malaysian guy who said to try Taobao was giving out incorrect info. He claimed that Rhine might have been producing frames for Pacific Cycles. In fact Pacific Cycles has nothing to do with Rhine China. PC has their own factory in Taiwan, given PC itself is an OEM manufacturer for other bike companies. Rhine bike frames also have slightly different geometry in comparing to the original Birdys, though some of their parts are interchangeable. Basically Rhine is a Chinese knock off of PC Birdy. I should have corrected that guy in the thread, LOL.
FYI, Taobao is like the Amazon in China. For foreigners you can use Aliexpress as an alternative.