Hello,

I have been scouring the internet for a DT series sentry droid miniature, and I happened upon this game and apparently you get 3 of them in the Heart of the Empire expansion. Are they made in a separate single pack, or is buying that expansion the only way to get them? Thanks in advance for your expertise.

They were only included in Heart of the Empire. Generally, if the figure is included in an expansion, it doesn't have a booster, and vice versa. I think (plain) Stormtroopers are the only exception.

Yes just the boxed expansion, and you get 4 of them.

There are eBay sellers that break up the box sets. Like this:

https://www.ebay.com/itm/Star-Wars-Imperial-Assault-Heart-Of-The-Empire-Figures-and-Deployment-Cards/122749754225