Weirdly you can't & the original (blue logo) boxes are pretty expensive second-hand. I got mine new from a HUKD post about three years ago for £20 & it's still one of my favourite things - you can pause both live TV & NowTV streams, rewind either feed up to half an hour, it smoothly integrates all NowTV passes into the EPG so there's no faffing about, I can't understand why they removed the Freeview tuner from the later 4K (purple logo) model.
Best option ebay, as now tv no longer make the ones with Freeview HD built in.
No only the original Now TV Smart Box had freeview.
Back to being a busy bee again unfortunately (embarrassed)
Does anyone know if you still can get the now box with aerial port on the back to receive freeview channels has well.