Many thanks for you help @Yeshwanth it put me on the right track. The API does have a filter option and that looks like it complies with rfc7644 but my attempts to use it were rather hit and miss - I suspect as the API is preview it is not fully implemented. Getting the info out of the API was enough to allow me to parse the json using jq to get the list of users with the "allow-cluster-create" privilege. Here is the code running in a linux bash prompt to get the list of users with the privilege.
$ databricks api get /api/2.0/preview/scim/v2/Users| jq '.Resources | map(select(.entitlements != null and (.entitlements | any(.value == "allow-cluster-create")))) | map(.userName)'
This was so much easier when there was a page in the GUI to show entitlements ... Is it hidden now of have I just lost it ?
Kind regards, David