Magic was selling AT rental gear from last season... so I assume they will rent AT gear again. Super uphill-friendly resort, you get a free lift token for every uphill lap you take!!
Bolton valley has an extensive backcountry program, I have to imagine they'd have AT and splitboard rentals, and cool terrain to use it!!
Ski the Whites is a touring specific rental and guiding outfit with their base at Black Mountain NH. They host a 'Friday Night Lights' uphill series on Black Mtn. Wish I were closer, they're doing great things it seems.
The manager of Potter Brothers Jiminy Peak location was talking about hosting before/after hours AT events at Jiminy.