The best chance of the Astros obtaining a front line guy is Keuchel returning to 2015 Keuchel form.
Keuchel's last 5 starts (basically the month pre-All-Star break):
3-0, 2.78 ERA, 32.1 IP (between 6-7 IP each start), 10 ER, 30 H, 23 K, 8 BB.
That averages out to 6.1 IP, 2 ER, 6 H, 5 K, 2 BB.
His average start last year? 7 IP, 2 ER, 6 H, 7 K, 2 BB.
Small sample size, sure, but encouraging results.