I think you have covered all the ones I immediately thought of: quite a comprehensive answer. 👋As far as I know, no one brand sell the same model in OO and HO. However, some HO UK trains can still be found in second hand shops and on Ebay. The Fleischmann Class 42 Warship and Bulleid coaches, and old Lima Class 33 and Mk1 and Mk2 coaches and some wagons (but with rather coarse wheel flanges). Roco made a Dutch version of the Class 08 shunter, and the USA 0-6-0 tank is available in HO and in OO. Brekina have recently releases HO scale Routemasters, and various brands have HO British cars, vans and lorries, even RHD versions. Some brands had, or still have, various continental ferry wagons in HO, and one brand made the Type F Wagon-Lits for the Night Ferry train in HO. For the modern scene, variously liveried Class 66s are avalable in both scales.
Have you seen this website? http://www.british-ho.com/ Very interesting.
As for importing and shipping, I dare to assume that you are in the UK, and you are right. Shipping costs to the the UK have shot up due to Brexit, and of course inport duties and VAT may also be due, again, due to Brexit. I'm not trying to rub it in, but there it is.
The only non-UK OO scale models I can thing of would be Irish models, for example, the recent Accurascale Class A diesel and Mk2a-based coaches have also been announced. Of course, due to Irish broad gauge, they are even more "wrong" than OO is - they should use 20mm gauge track.
There were a few British Trix/Lilliput items that were an intermediate scale of 3.8mm to 1 foot. That included a Britannia, some BR Mark 1 coaches and Mark 1 Pullmans. By the time they did 'Flying Scotsman' they had shifted to full 4mm scale. There was a commercially available Korean brass 'Flying Scotsman' in HO as well - the brand name was something like Samhongsa, from memory.