What I’m looking for is some type of USB adaptor or similar thing that I can use with a few Raspberry Pi’s to create a 802.11 ah network, but Googling hasn’t helped at all. Does anyone know how I might be able to get HaLow to work?
This may be dated, but there are offerings now  for balcony cards for the 3B+ & 4s from multiple vendors.
Here are a couple:
There are more, but I am still evaluating them for a Project I oversee. I will return with more that I think are valid as I go through them.