My name is Jade, I am with the Social Care Team at Shopify.
There is a print on demand app in the Shopify App Store called Art of Where that does allow you to print on what they call "Athletic Crop Tops". You can view the product details which are similar to a sports bra but a little longer here.
I took a look at our other Print on Demand apps but was not able to find one that printed on sports bras.
Have a great day!