What is the purest silver available that is not part of another product like earphones?

You can get 99.9% pure silver bezel strips. Jewelry supply places have them.

At my place of employment we purify silver to 4 nines, or 99.99% for use in raw materials for electronics.

You could probably purify it as high as 6 nines (99.9999%) but it would be expensive and as far as I know there’s no use for it.

You can get 99.999% pure bullion, but the additional price of that fifth 9 isn’t worth the effort for most applications.

I used Alfa Aesar when I need specific materials. They are great.
Search for “silver”. You will find any purity you need, in any form: powder, shot, slug, foil, wire, etc. to 99.999%