You can download your Form 1099-R by logging into your account online: https://www.opm.gov/retirement-services/my-annuity-and-benefits/services-online/.
You can also call them and request that they send a copy of your Form 1099-R at (888) 767-6738.
Edited to add: I just wanted to let you know this is the correct number but it isn't working right now because they are experiencing high call volume. They indicate this on their website as well.
[Edited 02.01.2019| 4:05PM]
