How can I filter customers by sales channel for my newsletter?

[MargueriteJZest]

Hello,

I have a brick and mortar store, but we also sell online (www.zestbillings.com). 93% of our sales come from our POS system, but online sales have been picking up now that I'm paying for Google Shopping ads.

For my newsletter, I would really like to have separate segments for online customers versus brick and mortar customers. They have different motivations for shopping with us, and require different incentives for future purchases. I've tried applying location filters based on the customer's city or region, but some of our POS customers have a city in their profile and others do not. I've also tried filtering orders by sales channel, but I don't see a way to export customers based on that report.

What I really need it to be able to apply a filter customers based on sales channel. Yes, there will be a small handful of customers who have placed orders online and in store, but it's such a small number I could manually pick which marketing channel to put them in to. 

Based on the existing filters within the customer reports, I can't find a way to do this.

Perhaps this is something I can accomplish going forward with a customer tag by manually tagging online customers when orders come in (a little tedious given our online sales volume, but not unreasonable). I would just like to find a way to "clean up" my existing newsletter subscribers so that I have a better list of people who've actually visited our store in person in the past.

Any thoughts or suggestions?

Thank you.