You kind of have to go seek it out track by track, most of his acoustic work (aside from acoustic parts on "Midnight Rider" and "Revival", etc) was on session work, the highlights of which are on the Anthologies or the Skydog boxed set. Outside of that, check out Delaney & Bonnie Motel Shot, it features a lot of acoustic folksy and spiritual music with Duane on acoustic (along with Leon Russell, Joe Cocker and others singing backup and clapping). Also check out the whole Delaney & Bonnie A&R radio show that features Duane on acoustic (and King Curtis)

You can also find a comprehensive list of credits at http://www.duaneallman.info/duanediscography.htm

Thanks Bob for this link, very nice.

Yes, thanks again for posting this. Excellent stuff!!