Thanks to Robbie and Julian for your answers -- good explanations,
and good info on the links provided.  That leaves my other question
outstanding then:  How would I, as an end-user (not a someone who
has a roll scanner or puncher), take advantage of this?

A perfect example:  I'm in love with Play-Rite's rendition of "Music
Box Dancer".  I've gone through three copies now, and the fourth is
defective.  So, I'd like to pay someone who has an e-roll or archived
copy to make me a newly punched roll of this item.  Do we (end-users)
have a way of knowing who has what, and who can punch what?

For sake of argument, assume that at least someone out there has a copy
of this roll.  If not, assume I'm talking about a roll that someone
_does_ have archived. :)

Mike Morrey

 [ A large archive of piano rolls in electronic format (e-rolls)
 [ is presented at http://www.iammp.org/rolldatabase.php  At
 [ http://www.iammp.org/rolldatabase.php?showpage=37&sortby=title 
 [ you can find "Play-Rite 41141 played by Walter Erickson".
 [ This piano roll performance is copyright 1979 so you will have
 [ to arrange for a new paper copy through the copyright holder,
 [ Play-Rite (John Malone).
 [
 [ Performances copyrighted before December 1923 are now in the
 [ public domain, for example, "The Sheik of Araby", (C) 1921, at
 [ http://www.iammp.org/rolldatabase.php?showpage=48&sortby=title 
 [ Any of these performances could be perforated as a recut by
 [ roll punchers like Ed Gaida, Tim Baxter and Keystone Music.
 [
 [ -- Robbie