I use Chicago Canvas in the States.
https://www.chicagocanvas.com/produc...as-tarpaulins/
a 14" x 20" is US$ 154.95
a 16 x 20 is US$ 176.95
or by the yard and you sew hem and add grommets -
Color Canvas 15oz 10 Yard Roll
$119.00
100% cotton fabric
Double filled duck weave; stiffer & more durable than single filled duck
Non-water repellent
15 oz per square yard
10 yard roll
5′ wide
Available in stock colors: Black, Red, Royal
Special Order all other colors (only available in 10 yd bolts) - they do have tan, brown and olive available
Colors not guaranteed colorfast