Where can I find a USB to jack adapter for Lets Sing (Nintendo Switch)?

I have old Singstar microphones (Playstation 2) and would like to use them with my switch.
When I use the PS2 adapter, the microphones seem not to be recognized.
Can I buy adapters for the switch anywhere?
I haven't been able to find any that are sold without a Mircophone.

Such adapters are not recommended. USB to jack is not that easy anyway, you should use an interface the other way around.