The brake flexi hoses on my mini front wheels come out of the hub pointing directly towards each other but slightly upwards. Can I get an adapter of some sort so that they point forwards by, say, 30°

dunno but I think you will need to convert to banjo fittings since the final position of any screw type fitting will depend on the positon of the thred cut. - or you need to buy a few and hope the thread is cut differently to find the ones that fit best.

pretty sure I have seen angled banjo fittings ....

I can do you flexies with a "swivel" end (with a bend on as well if you want) so you can orient them any way you want. HTH