The only consistent way to listen to blues in instrumental form that I can think of is 'Jazz-blues.' A few titles that spring to mind are John Coltrane 'Plays the Blues' (Atlantic), Wynton Marsalis 'The Majesty of the Blues' (Columbia) and Lionel Hampton 'Just Blues' (not sure of the last title or label). There is a LOT of blues-influenced Jazz to be found. True "Blues" (sorry, couldn't resist the pun) IS vocal-based. That's why they call it "singing the blues" :-(
