My father bought a German-made P226 about 1994, and put it in his safe. He passed two years ago, and it came to stay with me, probably unfired.

I saw an advertisement at RTG for "SIG P226 9MM 4.4" RXP SLIDE ASSEMBLY $529.99
WITH ROMEO 1 PRO AND XRAY3 SUPPRESSOR
SIGHTS". I have been experimenting with 1911 Bullseye guns with tube red dots, and LTT Berettas, and I bought one of the P226 slides. My gut tells me to buy a dedicated barrel to go with it. Is there anything else I need to get to put it on the P226?

You do not need to buy an extra barrel. The original barrel and recoil spring should work in either slide. I have an extra slide with Romeo One that I purchased about two years ago, and it readily interchanges with my West German P226(9mm) and the new P226(40S&W). Mine was purchased as a complete upper, with barrel, recoil spring, and guide rod, which speeds up the changeover by a few seconds, but I have used it with either barrel with no noticeable difference in accuracy. So now I can shoot 22LR, 9mm, 9mm w/Romeo One, 40S&W, and 357 Sig from the same gun using different barrel and slide combinations.

I for one, would like to see pics of this unfired W.German P226. If 1994 vintage, it will have a 'KE' Proof/Date code on the slide.

My very first handgun was a 'KE' W.German SIG P226, and it's still my favorite pistol!

and wouldn’t shoot an unfired 94.