JR1572, the only place I know to get thoes componets is Olympic arms. but they might not sell just the barrel/bolt combo. I'd either look for a S&W upper, or and OLY upper.
I have a partially completed 5.45 barrel and bolt that Kurt (of KKF) was working on for me before he died. If you know a good machine shop that can finish the work, I'll cut you a good deal on 'em.