I already have a Sig 556R Gen 2 that takes AK mags and I wanted to get another Sig that also took AK mags.  I was hunting on Gunbroker, but the prices for the 556xi Russian and the 556R seemed too high at the time.   I went to my local gun shop and they had a brand new (old stock) Swat model with the aluminum handguard that looks similar to the Gen 1 MPX pistols/rifle handguard.    It is the proprietary SIG rail that you can screw rail sections into.

I am not sure if the 556R Gen 2 came out before or at the same time they transitioned over to the 556xi Russian.   Anyone know?

Any accessories still available for the 556xis?  Seems very slim pickings when Googling.

I only paid $1299 for it, which is many hundred dollars cheaper than they were a year ago.

Very little was ever available for the 556xi, even when they were fresh and in production.  About all I remember was you could get was the polymer handguard if yours came with the aluminum proprietary handguard, but even that became harder to find over time.  That’s the only accessory that I ever found for mine when I bought it new back in the heyday.