Are there any organizations that provide ongoing preparation for Kohanim to immediately assume their priestly duties upon the arrival of Moshiach? I would imagine that performing the sacrifices and mixing the incense would require some hands-on experience in addition to reading Jewish texts.
There's a really great website called: http://kehuna.org/ that contains a lot of materials online.
There is another organisation in Israel called the Temple Institute http://www.templeinstitute.org/
They are extremely right wing, and regularly promote Jews going to pray on the Temple Mount, which most Rabbanim don't allow. They have prepared many Kelim for the Beis Hamikdash, however, and there are no other organisation quite as involved.
As for (more contemporary classic) texts: The Chofetz Chaim urged Kohanim to learn these Halachos to be prepared for Moshiach to come. His son in law wrote Avodas Hakorbonos. The Aruch Hashulchan also penned a work, Aruch Hashulchan Heasid.