Where to buy propane hose that connects

those little round propane tanks you can get at Lowe's or home depot or Walmart (20 pound tanks) to the motorhome tank. I know they are different connectors but without knowing the names I don't know where to look. Not talking about those 14 oz green ones for the grill but the bigger ones that are outside in a cage.

thanks in advance,

Jimbo

PS Just thought it would be nice to have that hose available incase I don't want to move but need some propane.