Nick here from Shopify.
I took a look through some of the most popular print on demand (POD) apps to see if any of them had denim jackets and doesn't seem like they do. The apps I checked were Printful, Printify, CustomCat, and AOP+ Easy Print. From experience, I would say that denim jackets are probably too expensive and too complicated for POD fulfillment services to work with. I'd say your best bet in this instance would be to look up some third party wholesale shippers.
You can see some denim jacket wholesale and manufacturers below:
Hopefully, this helps and points you in the right direction for the next steps!
All the best, Nick
Really great shout @shaboom_Room, I just took a look and it seems like they do.
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