There's a lot of it on eBay. Here's a link to just one listing:
http://www.ebay.com/itm/50-Colors-Me...item35d02ddc83
Dharma Trading also carries wool roving:
http://www.dharmatrading.com/tools/c...ol-roving.html
and JoAnn Fabrics online has some too:
http://www.joann.com/martha-stewart-.../11116530.html
Amazon also has listings for wool roving.