There won't be a scripture address this issue because the Bible was not written to people under democratic government. The question is not whether "we" are to provide but whether or not government is somehow exempt from certain moral requirements.
Some close examples, though:
Deut. 26:12. When you have finished paying the complete tithe of your increase in the third year, the year of tithing, then you shall give it to the Levite, to the stranger, to the orphan and the widow, that they may eat in your towns, and be satisfied.
The tithe was essentially a tax under a theocratic government.
Isa 10:1 Woe unto them that decree unrighteous decrees, and that write grievousness which they have prescribed;
Isa 10:2 To turn aside the needy from judgment, and to take away the right from the poor of my people, that widows may be their prey, and that they may rob the fatherless!
Isa 1:23 Thy princes are rebellious, and companions of thieves: every one loveth gifts, and followeth after rewards: they judge not the fatherless, neither doth the cause of the widow come unto them.
Pro 31:9 Open thy mouth, judge righteously, and plead the cause of the poor and needy.
Amo 2:6 Thus saith the LORD; For three transgressions of Israel, and for four, I will not turn away the punishment thereof; because they sold the righteous for silver, and the poor for a pair of shoes;
Jer 22:15 Shalt thou reign, because thou closest thyself in cedar? did not thy father eat and drink, and do judgment and justice, and then it was well with him?
Jer 22:16 He judged the cause of the poor and needy; then it was well with him: was not this to know me? saith the LORD.