Lots of screens to browse on projectorscreen.com, with a good search filter.
Draper, Elite Screens, Elunevision, Visualapex on Aliexpress, XY Screen on Alibaba, all have 150" 1-1.3 gain tensioned motorized screens ranging from $1600 to $2200.
The 1 to 1.1 gain screens are typically fairly accurate. They'll probably have a .1 gain drop off towards the edges of the screen, unnoticeable. The 1.3 gain screens will have a larger dropoff. On that projectorscreen site they show the half gain graphs for alot of the materials. The draper matt white 1.0 and purewhite 1.3 are good references.