Terraform. Finding combinations for for_each when one of value should be got to know

Question

I would like to create a droplet with each of the provided regions from the already present image (snapshot). But it needs to find out the image ID in each of the regions.

I don't know how to find combinations for for_each when one of the values needs to get to be known.

locals {
  regions = toset([
    "tor1",
    "sgp1",
    "sfo3",
    "lon1",
    "fra1",
    "blr1",
    "ams3",
    "nyc1",
    "nyc3",
  ])
}

Getting image ID in a region

data "digitalocean_droplet_snapshot" "web-snapshot" {
  for_each    = local.regions
  name_regex  = "^s-sites"
  region      = each.key
  most_recent = true
}

This code doesn't work. Creates droplet in a region with image IDs in these regions.

resource "digitalocean_droplet" "stop-sites" {
  for_each   = local.regions
  name       = "${var.server_name}-${each.key}"
  image      = 102913678 # we should find the ID of image
  region     = each.key
  size       = "s-1vcpu-1gb"
  ipv6       = true
  backups    = false
  monitoring = true
  droplet_agent = true
}