Wouldn't you normally go to an old distro .iso and take the gnupg binary from there? What OS & version are you working with?
example, gnupg1-1.4.23-7: https://archives.fedoraproject.org/pub/archive/fedora/linux/...
example, gnupg1-1.4.23-7: https://archives.fedoraproject.org/pub/archive/fedora/linux/...
FROM openjdk:8-alpine RUN apk update \ && apk fetch gnupg \ && apk add gnupg
or https://alpine.pkgs.org/3.15/alpine-community-x86_64/gnupg1-... ?