I'm trying to find a painkiller to round out my armor's auto injector (currently, I have two doses of Jazz, a dose of Cram, and am planning on getting a dose of K-10 for when the "it's not mud" hits the fan in the hardest way humanly possible) but have found nothing. I've looked through all the drugs and the medical tech and found nothing. Is there a decent pain killer that I can use in an auto-injection unit in Shadowrun 4e? I'm finding this absence of liquid painkillers to be very odd.

Closest thing I can think of is a injection of medical nanites.

What you are searching is Bliss and Novacoke. Both provide High Pain Tolerance 3 with some other effects.

Hmm, Bliss should do nicely. Thank you kindly good sir.