Can I get his income tax refund to recoup backpay child support?

Yes.  Under Federal law, you can have his income tax refund seized for back child support.  You should contact the child support enforcement office to enroll in your state’s “tax intercept” program.  The law also applies to any Federal stimulus payments he may have received.  However, if your ex-spouse has remarried, the only portion you are entitled to from a tax refund will be the portion based on his income, not his current wife’s.  Your state’s child support enforcement office will hold your ex-husband’s tax refund for six months.  For more information, talk to a family law attorney and your state’s office of child support enforcement.