Two sum with two lists
Assuming that your lists are sorted and this is something that comes out of problem description and the part where you need to find something in 99% of that kind of questions you want to use binary search. So basically all your code could be written like this:

from bisect import bisect_left


def binary_search(a, x):
    pos = bisect_left(a, x)
    return pos if pos != len(a) and a[pos] == x else -1


def two_sum(a, b, target):
    result = []
    for num in a:
        index = binary_search(b, target-num)
        if index != -1:
            result.append((num, b[index]))
    return result


Now if you want to save some memory, you might want to make two_sum a generator, which will make it look like this:

def two_sum(a, b, target):
    result = []
    for num in a:
        index = binary_search(b, target-num)
        if index != -1:
            yield num, b[index]


I cannot really call my answer a review to your code because I completely overwrote a solution for this. But as I mentioned in the beginning whenever a problem says something about sorted lists and searching on it, most likely you will use bsearch in your solution.