In the US, most hepatobiliary surgeons are either
a) Surg onc trained or
b) liver transplant trained
As dr. cox stated, there are a few places which may offer separate HB training, but they are not that common.
Some of the surg onc fellowships allow you to choose an area of focus and increase your case load in that area (i.e. at UPitt you can do a year of general surg onc, then the next yr specialize in breast, HB, melanoma, etc)