Many tire stores are staffed with young'uns who can only look up tires if you give them the vehicle they're for. Their computer won't have any listings for a Sunrader, Dolphin, Winnie, etc. Possibly for a Toyota C&C (1-Ton/DRW). If they can't be convinced that a tire size with no 'middle' (profile) number like 'our' 185R14 tires actually exists, have them look up the tire for a 1986 VW Vanagon/Westfalia.
If that still doesn't work, you need a better tire shop!
BTW, your old tires with '90' are more than likely passenger tires rated for 1323lb (@35psi).