We buy ours at Fabricland. They have ~12 colors and it fairly often goes on sale at 20-50% off so we keep an eye out for a good sale and buy next years in advance as we redo the seats every year.
Not a huge range of color selections but if they have one that works for you what they have is very heavy duty, good quality material. We have not had a rip yet and we have hundreds of people each year walking all over them, dragging scuba gear, fishing gear etc.