I am seeking a mechanism for reliable delivery of large blobs through a network of occasionally-connected hosts that can forward the blobs using available transport protocols.

I can't find it, though. Most of the networking materials I can find deal more with immediate-transmission networks, where the destination host is reachable at the instant that the source host transmits. (This isn't a catenet.)

If anyone knows of such a common or standardized system, please drop me a note.

sounds to me like email, where the sending host tries again and again over a defined period of time to delivery data. no? --- Or (God help us) UUCP if scheduling is a factor.