Not recommending anyone but from the blurred text 
it is
https://www.vistaprint.co.uk/propath/pre...?pf_id=372
No point downloading, all Ad*be formats, no good for Gimp. The template is only a square, nothing you can not do yourself.
edit:
I do not know printful, but a bit of info here
http://www.tomwademd.net/everything-you-...-printful/
including a low-res image of a template. Again nothing you can not make yourself.
it is https://www.vistaprint.co.uk/propath/pre...?pf_id=372
No point downloading, all Ad*be formats, no good for Gimp. The template is only a square, nothing you can not do yourself.
edit:
I do not know printful, but a bit of info here
http://www.tomwademd.net/everything-you-...-printful/
including a low-res image of a template. Again nothing you can not make yourself.