Currently we don't have custom paper sizes for Newsletter Templates. One workaround is to use the current file and make any changes you need. Once you're done, save it as a PDF, and then print the PDF on your Tabloid 11x17 printer and scale the content to fit the page.
The added benefit is you don't have to try and scale all the content, as it will do that for you when printing. That works for any Word document you're using that isn't as big as you'd like :)
I truly appreciate this wonderful resource, it never fails to provide something meaningful to add to our activity schedule every month. I love to share our activities too in the hope of sharing the joy! Thank you!