How can I apply for naturalization if I've been married before but my current husband is the one giving me green card?

Although divorce records are available directly from the court that granted the divorce, and I presume that you supplied copies of divorce documents to the USCIS when you applied for adjustment of status through your marriage to your current husband, a copy of that divorce decree should be unnecessary in applying for naturalization based upon either (1) five years of Lawful Permanent Resident status or (2) three years of Lawful Permanent status while married to a U.S. citizen spouse. Similarly, if you and your first husband filed joint tax returns, you should be able to get a copy of the transcript directly from the IRS and that would show your former husband's Social Security Number, but knowledge of his Social Security Number should be unnecessary in applying for naturalization based upon (1) or (2).