What 1099 form should my ex-spouse use to declare Air Force retirement funds given to me?

It would be reported on a Form 1099-R from the Air Force, so your ex could use the same form to nominee the portion of his distribution to you.  This assumes he will receive a 1099-R for the amount of funds that belong to your ex and your portion as well during the period he paid your directly.  Follow the instructions below.

Nominee returns. 

Generally, if you receive a Form 1099 for amounts that actually belong to another person or entity, you are considered a nominee recipient. You must file a Form 1099 with the IRS (the same type of Form 1099 you received).  You must also furnish a Form 1099 to each of the other owners. 

File the new Form 1099 with Form 1096 (this is a transmittal for the 1099) by mailing to the Internal Revenue Service Center for your area. (Provided on the Form 1096)

• On each new Form 1099, list yourself as the payer and the other owner, as the recipient. On Form 1096, list yourself as the nominee filer, not the original payer.  The nominee is responsible for filing the subsequent Forms 1099 to show the amount allocable to each owner.

You can go to the IRS website using the links below for the necessary forms. 

• Form 1096
• Form 1099-R