Grant,
As you say, Skywatcher and Orion Optics are probably the first choice people. I’m very happy with my 12″ f/5.3 Orion Optics Newt and the 12″ f/4 Skywatcher Quattro, though heavy, looks like an absolute bargain! Have you looked at the Teleskop Service pages? They show a few 12″ and 14″ tubed models. Their ONTC models have 3 mirror positions for moving the focus in and out if required. Focusers and other bits are customisable. Of course, given Brexit looming who knows how that might affect prices/delivery from Germany?! On the same page (at the bottom) they have the Boren-Simon PowerNewts (up to 12″) which are f/4 in length but have a 0.7x reducer to give f/2.8 across a 25mm diameter field. The TS page is here:
Martin