Originally Posted By mira.mikes
http://www.seatosummit.com/products/display/34


And here are two more airporters wich can serve as raincover too:
Bit lighter than Sea-to-Summit 370 g for midlle size
https://www.radicaldesign.nl/en/products/backpacks-and-hipbags/accessories/undercover

And this is included with backpack ... no idea if they selling it also separatelly:
http://en.wolfcamper.com/hiker-60.html

mira