I'm not sure if you mean only in the very literal sense of up-regulation of the receptors. If you're just asking about supplements that act upon GABA receptors, perhaps similar to how Benzodiazepines do, that opens up a lot more potential options.
Disclaimer
First off, supplements are the wild west. You know how "heavily regulated" pharmaceuticals are in this country? Do you know how totally dangerous and outright criminal these pharmaceutical makers are? Well, take that and remove a huge portion of the regulations and you're left with the world of dietary supplements.
This does not mean it is impossible to get what you need. It just means you have to put in the appropriate amount of time into research. You need to figure out what you need, then find someone who makes it and then verify that that manufacturer is trustworthy. For instance, you might be looking into Mushroom supplements. These are really popular right now.
Now, I'm no expert whatsoever. I know a little bit, but not wanting to misinform, an example: Mushrooms typically have what is called Mycelium, which in simple terms, is like the root system and then the Fruiting Body, which is the aerial part of the fungus. For some Mushrooms, you want the fruiting body. For some, the Mycelium is really the part you want. For some, a certain ratio of both parts is the pinnacle. You will find that unreliable Mushroom suppliers will sell "Mushrooms" that are actually an unknown admixture of Mycelium and the wood/grain it's grown on.
Paul Stamets is a hugely famous Mycologist with his own line of Mushroom Supplements that are sold everywhere. In the course of my own research, I had to find out that this guy, though reputable as a Mycologist, was basically selling C-/D+ level products. He wasn't scamming people. He likely became the victim of someone using his name then cutting corners. Who knows. The idea is, you need to be able to do research. You do not want to put the time and energy into a supplement regimen when you don't even know if you're consuming the supplement in the first place.
Saffron - This is a totally underestimated substance. I'm saying that not even knowing how much a given reader is estimating it to be. It really is that good in my experience. I was blown away by this stuff. If you take a Benzodiazepine, for instance and that drug is going to release a 4-6 hour burst of effect, I almost felt as if Saffron was taking that same total effect, if you will and extended it to a proportional effect that lasted all day.
For the best results, you need to get the right stuff though. You want to get the STIGMA, not the FLOWER. Cheaper brands will try to sell the flower as it is much, much cheaper then the STIGMA, however, the stigma holds the majority of the beneficial stuff. Great for depression, anxiety etc.
Kava - This stuff is very similar to Benzodiazepines/Alcohol in terms of its effects, though it is much more mild. It does not seem to produce major issues of tolerance, dependence or withdrawal. If good quality Kava is used, it doesn't seem to have any ill health effects either. It's great for relaxing, not necessarily for sleep specifically though.
Valerian, Passionflower, L-Theanine - I encourage you to do your own research. These are all different compounds, though I feel they are fairly related in terms of the effects produced.
Reishi Mushroom - This is very relaxing. It can be taken once or twice per day and i find the effects to be pretty long lasting.
If you're just looking for stuff to relieve stress or give you energy, that's different. There are lots of other options. You mentioned GABA specifically though and this is the stuff that came to mind for me.
ibb.co
