@Jordan Rivers, online British food stores or if you're lucky enough to have one in your area, they should have them now. My fave online is the British Food Depot. Gourmet grocery store might have them or as @GWarren suggested, a bakery.
We always have Christmas pudding although I haven't made one. Usually go with a commercial one. Mum always sent one from the UK but she's gone now so have to source locally.
Check the Holiday Episodes of The Great British Baking Show on Netflix or the Masterclasses for the same series - I know there's a Christmas cake in one of the episodes.