Frank's correct... etrailer.com is your go-to source for that kinda thing.
That said... is there anything stamped into the wheels themselves that would give you some info? There usually is. Look on both the outer & inner sides of the wheel. If so, snap a phone-camera pic of it so you can blow it up and make it easy to read... then type that info into Google, and you may find what you need yourself.
Last resort... jack it up, remove a wheel, and take it to any trailer dealer or tire shop, and they should be able to give you the info you need. Of course, they'll wanna sell one to you themselves... but that's your call from there.
2013 VOLTAGE 3200 (EPIC I & II)
2014 Ford F-450 PLATINUM