Ancestry.com doesn't have everything online, but if you think they might have something you want, visit your local Family History Center.They have a subscription and you can your use their computer.Volunteers will be happy to show you how to access and use Ancestry.
The death certificate should show the name of the funeral director and being a business you should be able to find them from online directory such as http://www.switchboard.comhttp://www.switchboard.com
Cemeteries don't always have "official" offices, if they are small.You might try to enlist the help of a genealogical society in that area.
Here is a site for genealogical and historical societies in TX, first one listed is Amarillo.
I don't see anyone listed on the RAOGK (Random Acts of Genealogical Kindness) site for Potter Co.So you might visit the Potter Co, TX GenWeb site.Down near the very bottom of the main page you can sign up for a Potter Co. discussion email list.Maybe someone on there couldhelp you.
Or, you might try the "Record Lookup" forum.Go up, click on My GenForum, find and click on General Genealogy, find and click on Record Lookups.