If you have beaten the main quest line , then the gates are closed,, some Alchemist in the towns may have some blood grass. You also might check back at some of the gates you closed,, sometimes you can still find some around the ruined gate even after it is closed.
There is also a Mod you can download,, the one with the Mages tower,, it will have its own garden that has blood grass.
Thanks, i will be sure to check everyting and if still noting i will download teh Mod.
EDIT: The Mod was great i got the cure thanks.