Reef Industries has some wedge shaped ones but I don't like them as well.
Just the first hit on google:(nl)http://www.northerntool.com/shop/tools/product_200365576_200365576?cm_ven=Aggregates&cm_cat=Google&cm_pla=Tarps%2C%20Covers%2C%20Canopies%20%2B%20Shelters%3ETarps&cm_ite=117800?ci_src=14110944&ci_sku=117800(nl)