Missing gradm-3.1-201608131257.tar.gz in deterministic build

[petertodd]

./build-iso.sh fails at:

Step 31 : ADD gradm-improved /home/builder/gradm-improved/
 ---> b856c2822089
Removing intermediate container 3d0a04153b5f
Step 32 : RUN chown -R builder:abuild /home/builder/gradm-improved/
 ---> Running in 72061adf02e2
 ---> 94bf2c63ada0
Removing intermediate container 72061adf02e2
Step 33 : USER builder
 ---> Running in 9a2ab5aa81e3
 ---> 1d3ad6f62221
Removing intermediate container 9a2ab5aa81e3
Step 34 : WORKDIR /home/builder/gradm-improved/
 ---> Running in 85fa4816335e
 ---> 9e726f1c5630
Removing intermediate container 85fa4816335e
Step 35 : RUN abuild checksum
 ---> Running in 43d5704fc896
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:--  0:00:01 --:--:--     0
curl: (22) The requested URL returned error: 404 Not Found
>>> gradm-improved: Updating the md5sums in APKBUILD...
md5sum: can't open 'gradm-3.1-201608131257.tar.gz': No such file or directory
md5sum: can't open 'policy': No such file or directory
md5sum: can't open 'base.policyd': No such file or directory
md5sum: can't open 'grsec-rbac.initd': No such file or directory
md5sum: can't open 'pw': No such file or directory
>>> ERROR: gradm-improved: md5sum failed
The command '/bin/sh -c abuild checksum' returned a non-zero code: 1

Found a copy here: http://deb.digdeo.fr/grsecurity-archives/gradm/, and manually changing the relevant URL in https://github.com/zcash/mpc/blob/f54c0db2d156ec602d0e26c6a63a36b6c7486b48/iso/gradm-improved/APKBUILD worked, but build scripts should be updated. Better yet, include a copy in the repo.