Could you confirm if the appIds you are pertaining to are the ones already targeted for a specific campaign or ad group? If so, retrieving of these appId's are possible, however, you can only retrieve this on a certain level (campaign level, ad group level etc.) at a time. You could use the
CampaignCriterionService.get() or the
AdGroupCriterionService.get() depending on the level you wish to retrieve this. You just have to specify MobileApplication.appId in the selector.
If you wish to retrieve the ones that are not yet targeted, I am afraid this is not possible in the AdWords API.