It doesn't need to. The U.S. publicly says it employs drone strikes in self-defense. That's covered under the Charter so that's enough. No additional supporting resolutions are necessary.
And Pakistan has publicly stated that it has offered to:
1. Conduct drone strikes based on US & Pak Intel
2. Conduct joint drone strikes based on US & Pak Intel
3. Conduct PAF Airstrikes based on US & Pak Intel
In the presence of these alternatives offered by Pakistan, the US argument of 'self defence in the face of Pakistan's unwillingness to act' has absolutely no validity.
And yes, the US does need additional supporting resolutions since the current argument you are making would allow any Rogue State to unilaterally launch hostilities under the guise of 'self defence/fighting terrorism', when that might not be the case. Such actions by Rogue nations (such as the US currently) are precisely why the UN Charter calls on any State claiming to act in 'Self Defence' to immediately declare any such actions in the UN, which the US has not done, which in turn means the US military actions in Pakistan carried out in the guise of 'Self Defence/fighting terrorism' are illegal under international law.
Of course, if Pakistan wanted to proclaim your position all it would have to do is speak up as it currently has a SC seat. I imagine the U.S. representative would then simply repeat what has already been said publicly but to an even larger audience. Pakistan hasn't done that, probably because it's just too embarrassing.
Pakistan has not done so out of a desire by the leadership to not escalate the confrontation with the US, the same reason Pakistan has chosen to not shoot down US drones, and instead diplomatically engage with the US to find a mutually acceptable solution to the disagreements between them - unfortunately, US dealings with Pakistan are reflective of Imperial Hubris, rather than any desire to cooperate and find mutually acceptable solutions.
A question: Could these be sourced from the NATO containers that allegedly went missing in Pakistan per a story several months ago? After all, the bara bazars are full of winter jackets and night visions goggles, are they not?
I thought weapons and sensitive military equipment (the NVG's etc., not the jackets) was shipped by air, not through the land routes.