I logged onto Tesla's website last night (and today) and did not see the Roadster listed across the top of their main page like the rest of their models. It could be I'm just blind or perhaps they are changing their website. But as of right now I cannot find a way to access the roadster order page.
*update* I can still access the roadster page if I google "Tesla roadster order page" and get to the page that way. However I do not see a link on the Tesla website page still. Perhaps it is just a website issue.
It's in the sidebar: They reshuffled the top navigation bar recently to focus on the products that they are currently selling. Cybertruck and Roadster were relocated to the slide-out menu on the side.