Level 56 and 58 items do produce Leaf/Landborne Aethersand, just not quite as often as level 60 items. I get them pretty frequently at 8/8, from all the reduceable items, and sometimes in groups of 2 and 3 just like from the level 60 items. I was struggling hard to get decent sand returns until I decided to just go for the level 58 item if it popped, and if nothing popped before I hit max GP and my cordial was ready I went for the level 56 item. I had all the sands I needed in no time after that, most of them not coming from the level 60 items.

Of course if you are specifically going for HQ, I'm pretty sure you need a level 60 item since I never saw HQ from anything else. But you should not be trying to use HQ Aethersand for every singe sand you need, since they are far too time-consuming and unreliable to get in the quantities you need. I remember needing 1 HQ Leafborne to make up for an NQ mat early on, and I spent literally 13 hours straight without seeing one. This last batch of sand I gathered, I saw an HQ within a couple nodes, and two more before I was done. RNG sucks and you really don't want to be trying to get full HQ sands for every single thing you craft. Beyond the accessories, the amount of extra HQ % you get per HQ sand is extremely small compared to the effort it takes to get one, and absolutely not worth the hassle.