Use academic search engines and try BASE or CORE Discovery, which specialise in Open Access content.
The University Library Basel recommends the following steps: a search for the full-text article using academic search engines, a search using browser extensions for Open Access, requesting information from researchers. And of course there is always the option to order texts via Copy orders, Courier or Interlibrary loan.
If you would like to publish something as Open Access, you can find information on our Open Access pages.