Best YOUTUBE video showing how to make an RCA Interconnect?

Another source if you live in a country they ship to is Take Five Audio - e.g. they do not ship to eastern europe - so check with them first
https://www.takefiveaudio.com/

I buy most all of my DIY materials from them. A lot of theri products are cryo'd as well (if you believe it makes a difference).

Often they ship same-day

Another is Parts Connexion
https://www.partsconnexion.com/

If you want to lok at some advanced geometries for IC's Speaker cables and Power cables take a look at...
http://image99.net/blog/files/category-002ahelix-interconnect-cable.html
http://image99.net/blog/files/category-002ahelix-power-cable.html
http://image99.net/blog/files/category-002ahelix-speaker-cable.html

Of the three the speaker cables are the best bang for the buck, but the IC's are extremely good also

The can appear overly complex, but you'll get the hang of it after winding the first Helix spiral :-)

They provide excellent sound quality

Regards - Steve

for wire , guess it all depends on what you want to spend ?

you could look at Parts Express has bulk wire and you could also check out VH Audio

https://www.parts-express.com/cat/bulk-wire-bulk-cable/2096

https://www.vhaudio.com

sure there might be some other sites that someone will mention.