Hi Scott,
Thank you for reaching out. Please see
here for the available metrics you can pull from TargetingIdeaService. Unfortunately, impression share isn't available. The service generates new keyword ideas based on the ones in your account so none of them should already exist unless you are using
RequestType STATS which shows metrics for existing keywords.
Regards,
Mitchell
Google Ads API Team

ref:_00D1U1174p._5001UV06Kz:ref