You can give a search on these websites!
This one sub cheap and they also got too many psd t shirt designs…
https://www.freepik.com/search?dates=any&format=search&page=1&query=t%20shirt%20design&selection=1&sort=popular&type=psd
http://xtragfx.com/index.php?do=search&subaction=search&story=t+shirt+bundle# <<< need to register to search and download, but make a temp account there, do not use original email:pass
https://psdkeys.com/logo-and-product-mock-ups/apparel/74432-100-t-shirt-designs-2037879.html
https://www.gfxtra31.com/adobe-photoshop/724983-cm-t-shirt-design-big-bundle-473387.html
https://graphicex.com/banner-mockup-template/12779-t-shirt-mock-up-bundle-7929614.html
https://allday1.com/index.php?newsid=270215
https://gfxcosy.com/print-templates-psd/flyers-posters/8832-crush-valentine-party-flyer-template-6532639.html
http://www.downduck.com/index.php?do=search&subaction=search&story=+T-Shirt+&sa=search
https://0lik.ru/index.php?do=search
https://freepsdfiles.net/?s=t+shirt+design
Note: Download at your risk, we do not own any of these websites!
!