I have found that my local classifieds is a great option. In the Northwest we have a website specifically for firearms classifieds. Many areas have such a thing. I am able to get a face-to-face sale of almost anything I need. I may need to pay somewhat inflated prices, but if you need it NOW, then you are by definition beholden to market prices.
.45acp, .40 S&W, 9mm, .38 Spl, .380 acp, 22lr
12 gauge, .223/5.56x45mm, 30-30 Winchester
2 Chron. 7:14 Christians must seek His face