Thanks for your suggestion.Hopefully, your friend should be able to get a 9x19 barrel. Barsto seems to have them but I don't know about exporting them to Italy. Plus they need a bit of fitting.
Sig 239 Barrels Archives - Bar-Sto
barsto.com
Maybe through Midway Italia, Brownells Italia or the SIG-Sauer italian importer which is Bignami S.p.A.
Bignami has the 9x19 barrels for the 9x21 P226 and P99 I have and I'm really tempted to get at least one. I'm pretty sure the Walther 9x19 barrel for the P99 is a drop-in while I think the SIG barrel for the P226 requires some fitting.