The 400/5.6 IF-ED also has a red dot.
The mirror lenses has no red dot. Some call them a poor-mans ED or APO lens. Don't know how they perform with IR.
Zeiss made for Hasselblad two tele lenses they called "Super-Achromat". A 250mm and a 350mm. With adapter they will work on a Nikon body.
Maybe they are cheap on ebay?
I remember Hasselblad wrote that even if light is IR or UV no focus compensation was needed on the focus screen.
Not very cheap but not impossible to get either:
https://www.ebay.com/itm/304582604379Older versions exists which are probably much cheaper.
I wonder how well corrected the new Z-teles are?