As to buying Romex at the big box stores, even when it was illegal to use in the whole County, they still carried it. One Department Manager told me that Corporate made those decisions without his input. He never sold a single foot of it amd had to explain his "poor performance" every month.
Romex is now recognized in Chicago, but you're not going to like the installation limitations.
"18-27-336.4. Uses Permitted.
Listed Type NM and NMC cable with listed fittings shall be permitted to be used only for limited extensions to knob-and-tube lighting or appliance branch-circuits in existing wood frame residential occupancies not exceeding three stories in height, but not where subject to mechanical injury as in new or remodeled building construction.
Type NM and NMC cable shall be permitted only in dry locations where concealed, in walls and floors of these occupancies."
Told 'ya you wouldn't like it...
That's similar to New York City. We're also big-time on BX (armored cable) for residential, especially multi-story.
Romex was recently allowed, but only on resi houses less than three stories.
You can buy Romex at the Home Depot here, but I've never seen anyone buy it. Smaller hardware stores, I've never seen them carry the stuff.
Plastic boxes, those are for the suburbs. Literally. You won't find them at your neighborhood hardware stores, or even Home Depot. Everything we use is metal.
My office building is done in pipe and BX and the new "luxury" high-rises sprouting up all over the place here use pipe. They lay it out for the ceiling of the flat below before pouring the deck.