Who cares about horn noises - It's the engines that are worth listening to not the horns!
You need to make the effort to get to places where engines power up. Even a class 70 sounds reasonable on full power, a class 60 even better, and there are a few 56's out there still. No need to mention how great they sound. Also don't forget about the classic fleet which is still just about hanging on - loud, clagging, thrashing 20s, 31s, 37s, 47s and 57s can still be found and heard. Engine noises do not start and end with 66s.
On the more modern side the 92s still sound great when the fans are roaring on full tap. Also don't forget the Paxman VP185 engined HSTs on the Midland Mainline. Its not all MTU just yet.
If you can't find the engine noises you want on the railway then I suggest you try the airfield, large air plane engines can sound impressive.
It has always been about the engines - horns will never be a substitute as far as I'm concerned!