To find high altitude bombers, watch the strats. At least during US prime time, there always seems to be somebody messing with the strats. Once you start making a habit of looking at strats, you notice the paterns of approach to them, and can estimate quite well when a dar bar 2-3 sectors away is headed towards them. If someone is already at the strats, they usually make several passes, and you can estimate where they are by which strats are blinking, and when you get close, by the ack puffs. Of course the ideal is to intercept them before they get there.
My problem is that I am no good at attacking bombers, but at least I can find them.
MH