How is it possible to get a new sponsor to submit the Affidavit of Support?

If the petitioner is not available, then you have to explain why since the law requires the petitioner to submit evidence of commitment. An alternative may be available if you can explain why the petitioner is not ready to provide support.

The petitioner is required to be the sponsor in a family case. If the petitioner doesn''t make sufficient income then an additional cosponsor may be used. If the petitioner is no longer sponsoring, then there is no case unless abused spouse, widow or certain other exceptions.

The petitioner in a marriage based immigration case must submit an I-864 affidavit of support even if they have no income. A qualifying cosponsor can also submit an I-864 and supporting documents, i.e., proof of U.S. citizenship or LPR status and most recent U.S. federal income tax return and W-2 form, to meet the financial requirements of showing that the beneficiary/applicant is not likely to become a public charge. Keep in mind that if the petitioner is not contactable in a marriage based immigration case, it is unlikely to be approved because there must be a bona fide marriage.

You should contact NVC.