issued a 221g after interview, how do we find out the "A #"

[Sharon+Larry 1]

Had my interview today but was issued a 221g after the interview. Now, my fiance needs to gather information to clarify what was filled in the I129F. On the question about, "has he previously filed a petition for a fiancee, husband/wife" - he answered NO. We discussed about this prior to sending in the I129F, he could not exactly recall those paperworks he had signed before. It was all done by his ex-wife. But I got him to declare her name to answer question no. 11 on the previous filing of Affidavit of Support. During the interview, according to the CO, they had done a background check and found out that he did file an I130 before. So what the CO wanted is to clarify is all about it. Reading back the I129F form, questions asked where: Petition previously filed for whom, when and where and the A #. We need your advise, if anybody knows, how does he find out about the A number? Thanks so much!