Books are optional for oaths. I know I didn’t have one when I was sworn into the military. In fact I expect that most oaths are taken without books, including, I’m going to guess, the ones for MPs.
From the Parliament link above:
“MPs take the oath by holding the sacred text in their uplifted hand and saying the words of the oath”. The text/book can presumably be whatever’s sacred to them (by default a bible), but I don’t suppose the authorities will hunt around for just anything.
They can use the Koran, the Talmud or other religious texts that are important to them.
I think that, for high-profile cases, the swearer will bring their own book. Which, yes, is usually a bible, but it might be a bible that’s been in their family for generations, or which has some other sentimental value.