Give this a try :
Go to unRAID --> Settings --> Community Applications --> General Settings
Find an option labelled "Enable additional search results from dockerHub?", and change the drop down to "Yes".
Click "Apply"
Then click "Done".
Go to unRAID --> Apps and locate the search field (top right hand corner of the Apps page)
Type "ib docker" (no quotes) and click the search button.
You'll be shown a Community Applications (CA) Search Page which states that there was "no matching content found",
Inspect the search page closely however, and you'll see a docker icon/logo in the middle of the page, with a link underneath labelled "Get more results from DockerHub".
Click the link and a short search will be then be conducted on your behalf, resulting in a list of potential apps from the DockerHub.
Select your preferred version, click "Add" and follow the prompts (same as adding a docker from the CA "Apps" section of unRAID)
Please note that Ryan Kennedy of ryankennedy.io has not published this app on DockerHub (his only public repository is DeepDream - last updated 2 years ago) so the specific code you likned to will not be shown in the search results.
However if I understand your intent correctly, I believe that a search conducted via the community applications "Apps" page will list several dockers for the same "Interactive Brokers" application, essentiually assisting you to achieve the same outcome (getting the IB app running in a docker on unRAID).
A casual inspection indicates that the 5th, or perhaps 8th app, in the search results might be worth a quick look.
Hope that helps