Here is a repository containing debian arm64ilp32 packages (aarch64, ILP32 ABI), built using rebootstrap. That includes both amd64 cross-toolchain packages (kernel headers, binutils, glibc, gcc-6, crossbuild-essential), and native arm64ilp32 packages to build an image.
The stable repo is here: ILP32 apt repository Add:deb [allow-insecure=yes arch=arm64ilp32,amd64] http://people.linaro.org/~wookey/ilp32/repo rebootstrap main deb-src [allow-insecure=yes] http://people.linaro.org/~wookey/ilp32/repo rebootstrap main
to install stuff. Unstable packages will be added shortly.
Sorry, none of it is properly signed or any of that fancy stuff - you'll just have to trust for now.
sudo debootstrap --foreign --no-check-gpg --arch=arm64ilp32 rebootstrap chroot http://people.linaro.org/~wookey/ilp32/repo /usr/share/debootstrap/scripts/stretch
which will give you a chroot in a 'chroot' directory.
You need a kernel with ilp32 support built/configured in to run this on either qemu or arm64 hardware.