use following script to get list of available options for docker-machine digitalocean driver:
#! /bin/bash
curl \
-X GET \
--silent \
"https://api.digitalocean.com/v2/images?per_page=999" \
-H "Authorization: Bearer $DECIHUB_DIGITALOCEAN_TOKEN" \
| jq '.' > do-images.json
curl \
-X GET \
--silent \
"https://api.digitalocean.com/v2/regions?per_page=999" \
-H "Authorization: Bearer $DECIHUB_DIGITALOCEAN_TOKEN" \
| jq '.' > do-regions.json
curl \
-X GET \
--silent \
"https://api.digitalocean.com/v2/sizes?per_page=999" \
-H "Authorization: Bearer $DECIHUB_DIGITALOCEAN_TOKEN" \
| jq '.' > do-sizes.json