I'm having no problems finding HGE's
You have to jump to the right system type. Then, scan the nav beacon. If HGE's are present, see if you have enough time to get to it. If so, go collect your mats. If not, jump to the next system and repeat. Some systems had 3 HGE's with 30 minute timers so I got all three of them. Most had only one or two. On average every third one was unreachable due to the short expiration timer.
I did a string of about 50 jumps and found 20 HGEs yesterday. In 3 hours of playing, I collected hundreds of G5 mats and traded for what I needed. Easy as can be and I have a ton more for other engineering projects. It's much more straightforward than flying in circles for hours. Additionally, I was able to get system scans for exploration credits too.
I have adjusted my game playing to always scan the nav beacons when I jump into a new system whether I am currently engineering or not. Any HGE's show up and I just go get them, then get on with whatever I was doing. It adds a few minutes to the time in system, but it's worth doing automatically so I'm never short of G5's when I need them.