Lots of places can supply awning hardware and/or fabric. Just Google RV awning and you should find several.
While typical RV awnings are 8 ft wide, the roller tubes are capable of handling greater widths. 10-12 ft should be no problem and 16-18 ft is a common length on larger RVs. If the standard awningpackage doesn't meet your size requirements, you can buy the hardware and fabric separate.
Here are some possibilities:
RV Awnings, Motorhome Awnings & Screen Rooms - PPL Motor Homes
ShadePro Inc.: RV Patio Awnings
Fun In The Shade-Custom RV Awnings
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL