My cousin whose mother is Polish says: “Trisodium phosphate (TSP) and
borax powder are common laundry aisle items. I’ve used grocery store
borax as a flux for brazing. Boric acid powder might be available in
a pharmacy, I know it has medical uses. Nitric acid and aqua regia
might be available at construction supply houses, I believe they are
used for etching brick and concrete.”
I haven’t spoken to his mother for the name of these items in
Polish, but I will this weekend.