From what I have seen when I have looked in the past there are plenty of 80 gph pumps available online, but pumps down in the 30 gph are hard to find. "Ultra low flow aquarium pumps" or "micro mini aquarium pumps" are some terms that you can use for your online searches. Most of these are cheaply made and I have found that there is a correlation in the longevity. Good luck and let us know what you find!
If you’re taliking about a variable flow power head, then Jebao make some small ones. Been a while since I used them so you’d have to search for the model number. They also appear to now have a Nero clone, which I’d imagine is small.
I use an Eheim CompactON 300 in my small FW tank which has been very reliable so far. Manually adjustable AC pump. Small form factor for a complete unit but not as small inside the tank as some more expensive options. May not provide enough flow for your needs however.