There's two nice tutorials on making sails here -
1 ~
2.
Simply, find some suitable material - I've used old tshirt stuff in the past, but anything that's tightly woven and the right thickness should work. Paint it with a mix of 5 parts water to 1 part PVA glue and let it dry (this stops it fraying, stiffens it, makes it easier to cut and draw on). I use a hole punch to punch out the holes to attach the sails to the masts - and trim the holes with nail scissors. Shoving a soldering iron through the cloth also works.
As for the printed stripes, I think the easiest way is to either find some appropriate cloth (which could be quite hard) - or paint/colour them on yourself. It'd be easier to do this before you cut the sails out.
It's possible to run pva-d cloth through a printer and get good results - though it does tend to clog everything up and go wrong an awful lot!
Hope this was helpful.