If I attack with a missile or torpedo that requires me to spend a target lock, do I still get Han Solo's ability to turn focuses into hits, or has the target lock been spent and no longer trigger?

No, once you spend the TL you no longer can use it for anything else.

That assumes ones you have to spend it on, and not others like homing missile which simply needs you to have one.

If you take it through step-by-step:

1. You spend the lock to fire the missile
2. Roll your attack dice
3. Defender modifies
4. Attacker modifies. Han would normally trigger here, but where's the target lock? Darn, spent it back at step 1.

Too bad. Not like you could get Solo on Redline.