Its really weird. Some of the auction sites have them, and some of the smaller retail sites have them listed, but out of stock
https://www.gunbroker.com/item/792956611The Sig site also has 8" barrels and 8" hand guards for sale, but there doesn't seem to be a prebuilt option for that configuration.
Its an expensive enough gun as it is. I don't know if it would be worth it to buy it, replace the barrel and handguard immediately (for $750 btw). And that's without even getting into how much it would be to SBR it and/or add a suppressor.
For years I've wanted to get a compact 9MM carbine. Its been.... surprisingly challenging.