I am using the Duet theme and have Custom Design CSS purchased and am hoping to add a subscribe and search button to the masthead. Is that possible?
In any WordPress.com theme, you can only add the follow blog widget and a search widget to sidebar areas which are controlled through your Appearance → Widgets page.
For the Duet theme, it has a layout option to turn the sidebar on or off under Appearance → Theme Options.
And if not either of those options can I create a page and have it be just a subscribe/search page where those options are in the center column and not just the sidebar?
Currently, it's not possible to add subscribe (follow) or search widgets to a page in WordPress.com.
There's a possible workaround to do what you are asking though. It does take some work, and I'd be happy to help you with it! What you could do is enable the sidebar, add the subscribe (follow) and search widgets you want, and then position them somewhere else on the page (like the header) while also styling out the space used up by the sidebar.
If you're interested in getting more help to try that out, please enable the sidebar in Duet, setup the widgets you want, and post a link back to your blog in a reply here.