I have the pleated day/night blinds in my Voltage.. and like you, the string broke in mine.
Camping World sells a "First-Aid" kit to repair it. It too is from United Shade, so I'm not sure if it's the same one you got. But if not, while a little tedious & time consuming (if I remember correctly it took me about 45 minutes to an hour to complete)... it worked as advertised when I repaired mine.
Here's the link:
If you want to try to find a direct replacement, I'd try calling or just looking it up at Trekwood Parts.
Just enter your year, make & model... and if it's available, they should have it.