Where do you live? In the US, there a lot of widely available brands of UL-listed (or equivalent) wire with clearly marked specs and the cross section in ridiculous units of AWG. If it says it’s copper and it’s not an outrageous counterfeit, it’s copper. (And it will have a resistance that is in spec, because this is important for code-compliant electrical installations, and it won’t corrode when terminated properly.)

And the UL-listed stuff is fantastic, because UL cares about the insulation and jacket. There is plenty of “speaker” wire with crappy insulation that degrades after a few years, but I’ve never seen an actual CL2 or CM or CL3 (or their R or P variants) or THWN(2), TC(-ER) etc, cable, from the last 30 years, with any such issues.

16AWG CL2 cable is fantastic speaker wire, and it’s cheap and you can buy it at any store that sells electrical supplies. TC-ER is great if you need something bigger than 16AWG (the longer the run, the thicker the cable you need to keep resistance below 1 ohm or so), but it’s a bit harder to find.

The thing that can be genuinely hard to find is nice twisted-pair or shielded twisted-pair cable in any format other than category (Ethernet) cable, and that tends to max out at 22-23AWG and may have the wrong number of conductors for whatever you’re doing with it. For making up an RCA cable, this is completely unnecessary — use RG59 or RG6 cable if you need particularly good shielding. But for long runs of balanced audio cable, you want actual twisted pairs, 23 AWG is plenty, but you may need those pairs shielded from each other to minimize crosstalk. So you end up with commercial snake cables, and those are not cheap. Some people use digital stage boxes these days, because an effectively transparent ADC and all the electronics needed to make it work can be cheaper than the fancy cables.

> Where do you live?

Somewhere far w.r.t. US. :)

> 16AWG CL2 cable is fantastic speaker wire,

Yet, it's way thinner than the manufacturer of my speakers recommend, which start at 13, and only go up. In my case I need 12 or 11. I don't remember honestly.

The good thing is, I managed to get a roll of the correct cable made by Acoustic Research. While the cable is not "fancy", it's copper, has the correct thickness and it's jacket still feels like day 1, and that thing is 10+ years old at this point.

For RCA cables I still use the factory default set came with my amplifier. Japan made, with very flexible jackets and gold plated connectors. That provides more than enough clarity for me.