While most sources of loot during the Pre-Season week of Midnight Season 2 are limited to Veteran or Champion track loot, there is one source that still gives you Hero track.
Delve Maps
The source is 
Trovehunter’s Bounty, also known as Delve Map. Upon using this and completing a Tier 8 or higher Delve, you’re guaranteed a Hero Track 1/6 piece.
How to Obtain Trovehunter’s Bounty in Midnight Season 2
There are multiple ways to obtain a Delve Map in Midnight, however, Season 2 added a very simple one. Completing Purging the Vaults, the weekly quest on Coiled Isle, awards a Trovehunter’s Bounty.
Note that you may only receive one map per week per character, so if the map isn’t a reward from the quest, it means you have already looted one this week.
Completing the weekly will also award you with one 
Venom-Cursed Fragment, which can be turned into a random Champion Track item when you combine two of them.