那裏可買到黑白菲林？

What brand of 黑白菲林 do you need? Kodak? Fuji? Ilford??
They should be widely available at all reputable camera stores like Wing Shing, Man Shing, Tin Cheung, as well as selective stores in Stanley Street, Central. Some professional labs (eg. ColorSix, East Asia) also carry B/W film of selected sorts, properly refrigerated.
If you can't find the film you want, maybe they are temporarily out of stock but should be available very shortly, given the demand among the prophoto community.