You don't/haven't provided the model number for your trailer, all you've identified is that it's a 2011 Passport Exp Hybrid. No mention which floorplan, size or weight. That said, the majority of 2011 Passport Express trailers use ST205 75R14 Load Range C tires. NOTE THE ST designation. You can confirm the size on the sidewall of any of your current tires. Also count the lug nuts on the wheels. It should be 5. I would also confirm that the "tire load chart" located on the driver's side front corner of your trailer designates the same size tire that is actually on the trailer. It's possible that a previous owner "cheaped out" and installed smaller tires than are actually called for by the manufacturer...
Any trailer dealer can obtain a tire/wheel combination in the wheel size, lug configuration and tire size.
If the tires called for are ST205 75R14 LRC, this link to Tractor Supply is one source for a "spare tire/wheel"... Note that Tractor Supply does not usually stock "the highest quality tire brands" but they are "cheap enough and readily available to use as a "spare to roll the trailer to the nearest tire store for a replacement.
Here's the link to a TS tire that would fit the specs for most Passport Express trailers (listed on the Keystone webpage):
https://www.tractorsupply.com/tsc/pr...c?cm_vc=-10005
ADDED: If you do some searching on the Tractor Supply website, you'll find that they carry a Load Range D tire in the same size, on the same wheel for $25 less. Most people, when they buy tires, "upsize" load range from C to D or from D to E to attain greater carrying capacity and/or to provide a greater safety margin.