Buying seed germination blankets larger than 4' x 50'?

I have a large swale (corner lot) that I need to prevent erosion on.
It's newish construction, and whatever the builder put in there did
not take. Doesn't help that we're in a drought (North Carolina).

Where can I, if they've made, buy seed germination blankets larger
than 4' x 50'? I see the DuPoint ones at Lowes and Home Depot, but am
wondering if there might be a landscaping supply company I could mail
order from.

Are seed germination blankets made any larger than 4' x 50'? And can I
simply use wheat straw for the walls of the swale/ditch (cheaper), and
use the blankets just for the center "floor" of the swale? Seems I'd
need lots of blankets, secured with landscaping spikes, to prevent
seed and top soil from washing away.

Is there another newsgroup more appropriate for landscaping questions?