I seem to be staying west of the Plains these days and having trouble finding my Super Trucker Gear™ out here. Some folks have been recommending the Petro in Ontario, CA (USA), but that place doesn't have anything. Very nice guy running there chrome shop, who'll make you up some custom seats, though. Is there any equivalent to Walcott or Joplin, MO out along the 5?
There are some local shops that do truck "goodies" around various areas. They are NOT located in truck stops however. You'll have to ask a Ca. local driver that has his truck looking good. You might check Alameda St. south of the I-10 in L.A. There are locally published truck mags that will only appear in a hard to find location with boo-coo ads. (and pics) The same with Bakersfield and Fresno areas. Good luck......