As to the favor cancels, most (if not all) of these cut squares are philatelic. The rates in the Colonies were such that legitimate, non-philatelic uses of stamp values other than the 3-, 5-, and 10-Pf stamps are uncommon. And when you do find them, they tend to be on full covers or postcards, as subsequent collectors left them intact to show they're legit.
I wanted to use postmarks on piece for these pages, as they show the full cancel and fit nicely with the design of the pages. So, in the end, I accepted that I'd have to accept some obvious favor cancels. In the end, they're contemporaneous and are legit postmarks on legit stamps, just obviously created for a collector of the time. And considerably more affordable.
As to sourcing, I got all of these off the German eBay
. Most of the postmarks for Karolinen are fairly common, so they're readily available. As I work on the other colonies, I'm have to keep an eye on auctionhouses, as some of the cancels are really hard to find.
As to the postmark samples on the page, I didn't pull those from the pieces. Those are scans from one or both of the catalogs that I use for these — Friedemann's Die Postwertzeichen und Entwertungen der deutschen Postanstalten in den Schutzgebieten und im Ausland: Handbuch und Spezialkatalog
(The Stamps & Cancels of the German Colonies and the German Post Offices Abroad: Handbook and Specialized Catalog) and the Arbeitgemeinschaft der Sammler Deutscher Kolonialpostwertzeichen's (ArGe) Deutsche Kolonien und Auslandpostamtämter Stempelkatalog
(German Colonies and Post Offices Abroad Postmark Catalog). I frequently pull postmarks when I can't find a good scan in my references, but luckily, both of these books have excellent samples of almost all colonial postmarks.
I use Scott/Prinz mounts almost exclusively. I'll occasionally use a Showgard if I need an odd size that Scott/Prinz don't make, but I prefer the Scott/Prinz as the black backing of the Showgard's is slightly translucent and seems a bit thinner.
As with most of my philatelic endeavors, when it comes to mounts, I might have a hoarding problem…