I want to convert my stainless P220 to a 10mm. I bought a complete 10mm slide but need the locking block insert to make this work. I can’t find a part number for this. Does anyone know what it is?

Not wanting to be the bearer of bad news, but I am anyway.

There isn't 'one' part number to the insert, because there are more than one inserts for the 10mm P220.

The insert for a DA/SA will not allow an SAO slide to move as it taller than the insert for the SAO that will at least allow the DA/SA slide to cycle manually. That was as far as I got with this, so I don't know if the SAO insert would lead to any issues feeding the ammunition into the chamber. The DA/SA that I was checking out was one of the early 10mm P220s made, so this may be a production change and not specific to the actions of the frame.

If you are able to find one. It may require additional fitting. This would just about make it more economical to get a 10mm P220 oughtright unless the Commies don't allow you to such a thing. The other option would be fitting a .45 insert, but that would be way down the list of options I'd consider.