You must first know when the person died and where they lived at the time they passed. The obituary would generally be published in the local newspaper. Many papers have online access to obituaries for recent years available for free or a nominal cost. In Van Buren the local paper is the Press Argus but with Fort Smith so close the Southwest American, Southwest Times or Times Record are also possibilities. The local public library is also a good resource for newspaper publications. You can contact most libraries via email online. Depending on the locality and available resources some libraries will do lookups and provide copies for free or a nominal fee. In other cases, you may need to contact someone locally to do a lookup such as the genealogical society or another researcher in the area.

Familysearch.org is also a good resource. Using their online Resource Catalog you can search (free) for availability of newspaper microfilm for the locality and order, for a small fee, at your local Family History Library.

It was by locating an obituary for my great-grandfather that I learned he died out of state and explained why I hadn't been able to get a death certificate as I had assumed he died close to home. Once I knew where he died I had no problem getting a copy of his death certificate.

Good luck!