"Or, perhaps less likely, have there been impacts in the last billion years that may have thrown such matter into space?"

I would guess that there is as much of such matter beyond earth as compared to coprolites found on earth:

" "When I saw my first coprolite ten years ago, I thought no way, how could something as soft as poop fossilize?," says Berkowitz. "But coprolites are found on every continent and from every geological time period. There's literally tons of fossil poop out there, and it's now recognized as priceless for helping scientists piece together the puzzle of ancient life."
....
Jurassic Poop also reveals that more than 1000 human coprolites have been collected from Hinds Cave in the Chihuahuan desert in southwest Texas, making the site the largest human coprolite cache ever found."
http://www.eurekalert.org/pub_releases/2006-11/mu-dij111506.php

And:
"The 75-million-year-old fossilized feces, formally known as a coprolite, was discovered in the late 1990s near the town of Onefour in southeastern Alberta by Wendy Sloboda, a freelance paleontologist who is currently leading a paleo-tourism tour in the Gobi Desert.

Ms. Sloboda also has the distinction of co-discovering the T-rex coprolite.

"She's got a very good eye (for coprolites)," says Karen Chin, the world's foremost authority on dinosaur coprolites.

Measuring in at 64 centimetres in length (slightly narrower than the width of the average kitchen stove) and up to 17 centimetres wide, the six-litre bulk of the Albertan coprolite rules out small dinosaurs from contention as the probable pooper, says Ms. Chin, who led the analysis of the specimen.
...
"Under the microscope I could see these impressions and I thought, whoa! It looks like muscle tissue, but it can't be muscle tissue, that would have been digested," recalls Ms. Chin...
....
Preserved dinosaur soft-tissues, such as muscle and connective tissues, are extremely rare and are usually found in association with bones and some very well-preserved carcasses. However, when Ms. Chin took high-powered scanning electron microscope images of the coprolite, the images revealed the tell-tale parallel cell strands and longitudinal striations of muscle."

"Coprolite mining
In 19th century England, coprolites were mined on an industrial scale for use as fertiliser due to their high phosphate content.
...
The industry declined in the 1880s but was revived briefly during the First World War to provide phosphates for munitions"
http://en.wikipedia.org/wiki/Coprolite

"And finally the most pressing question of all: is there any way we can get it back? "

I think we should try to get our shit back, I don't know about getting all of it back, but some of it.

And yes we can, if we dream.
Vote Obama!