I want to file an extension to file my 1120S return later than the March deadline. Where do i find that form?

https://ttlc.intuit.com/questions/1900876-how-do-i-file-an-extension-for-a-corporation-partnership-t...

You must use TurboTax Business to file an 1120S return:  https://turbotax.intuit.com/small-business-taxes/

"Where do i find that form?"

Form 7004, which is included in TurboTax Business.

https://www.irs.gov/pub/irs-pdf/f7004.pdf