Alternative to Threadless?

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I have been trying to sell designs to Threadless T's for a while now and when I first started they were really good about offering specific reasons above and beyond their form letters for why they declined a design. But recently when I ask for more specific reasons, because the reasons in the form letter don't even apply, I have been completely and thoroughly ignored. My designs really aren't in the same style as the designs on Design by Humans and that's the only other site I've found that prints, markets and sells submitted designs. I could list them on CafePress or Custom Ink but those sites don't market for you. So I'm looking for another site that is similar to Threadless or Design by Humans where I can try submitting my designs for print.