Those can be found at Camping world or other RV stores (might require a catalog order). We bought ours for the house shower at Lowe's but the RV store ones will be lighter in weight and will probably fit the shower stalls better than the hardware store ones.
These are nice because they widen the area in the shower to provide more elbow room but they don't help make the shower taller. Don't hang it too high or the shower curtain might not fall back into the shower and prevent the floor from getting wet. I believe I've seen that the RV ones will also reverse so that it folds into the shower when you want more room after you are out of the shower.