Download source RPM package on Fedora system

I’ve installed Brave on Fedora 31 system by adding repo data and invoking DNF.
So I have:

$ dnf repolist

repo id                                                         repo name
brave-browser-rpm-release.s3.brave.com_x86_64_                  created by dnf config-manager from https://brave-browser-rpm-release.s3.brave.com/x86_64/
...

and:

$ rpm -qi brave-browser

Name        : brave-browser
Version     : 1.3.115 
Release     : 1
Architecture: x86_64
Install Date: Wed 12 Feb 2020 03:26:55 PM MSK
Group       : Applications/Internet
Size        : 257261143
License     : Multiple, see https://brave.com/
Signature   : RSA/SHA512, Tue 11 Feb 2020 01:25:12 AM MSK, Key ID a8580bdc82d3dc6c
Source RPM  : brave-browser-1.3.115-1.src.rpm
Build Date  : Mon 10 Feb 2020 03:32:55 AM MSK
Build Host  : ip-172-31-4-133.us-west-2.compute.internal 
Relocations : /opt 
Packager    : Brave Software <support@brave.com>
Vendor      : Brave Software, Inc.
URL         : https://brave.com/
Summary     : Brave Web Browser

but:

$ dnf download --source brave-browser

enabling fedora-modular-source repository
enabling updates-modular-source repository
enabling updates-source repository
enabling fedora-source repository
enabling rpmfusion-free-updates-source repository
enabling rpmfusion-free-source repository
enabling rpmfusion-nonfree-updates-source repository
enabling rpmfusion-nonfree-source repository
Last metadata expiration check: 0:18:26 ago on Wed 12 Feb 2020 03:32:07 PM MSK.
No package brave-browser-1.3.115-1.src available.
Exiting due to strict setting.
Error: No package brave-browser-1.3.115-1.src available.

I’m pretty sure that default system repos are configured correctly, for example,

$ dnf download --source coreutils

works just as expected.

So, how to download source package which was used to build binary RPM installed on the system?