#1
Hey looking 4 some good fairly easy blues guitar riffs for a two-piece guitar band or even just for a solo preferably in A or E but fine in other keys thanks
#2
The basic blues measures?

Lots of Led Zepplin songs have solo-over-able riffs, or just Voodoo Child it up.
#3
Look into
...

Muddy Waters
T-Bone Walker
Clapton
The Yardbirds
Cream
Buddy guy
Basically any music before 1975 that wasn't pop or jazz
#4
SRV.

Learn Texas Flood, His Version of Little Wing, Pride and Joy, and Rude mood, You'll have enough riff's. I guarantee it.