Here are some Mauser 3000's. Does your rifle look like any of these?

http://www.gunsamerica.com/guns/976229586.htm

http://www.gunsamerica.com/guns/976551397.htm

http://www.gunsamerica.com/guns/976556509.htm

If you read German (which I do), you'll find this page interesting. It's the Heym website, where they mention having made the Mauser 3000 rifles:
http://www.heym-waffenfabrik.de/S_Ueberu/S_Gesch.html

Here's another tidbit. The rifle is very similar to the Heym SR-20 (http://oldguns.net/cgi-bin/f2f/f2f.p...et/q&a5_04.htm):

"...Heym has been manufacturing classical Mauser type sporting rifles for many years. The company was first established in Suhl Germany in 1865. After WWII Heym moved operations from Suhl to the Bavarian town of Munnerstadt, were in 1952, the first post-war firearms were produced. In 1996 operations were moved again to Gleichamberg.

Early Heym post-war rifles were built on refurbished military actions, later actions were manufactured by FN. Heym also built modified rifles for Mauser (q.v.) before their SR-20 series was introduced in 1975.

...Barrels were 24 or 25 inches in length and made of Krupp steel. Importation of SR 20N rifles was discontinued in 2001. The blue book lists values for SR 20N rifles from $650 to $2000, depending on condition."

This is what I've dug up, and I keep looking. An old Montgomery Ward's catalog from about 1970 would be helpful, too.

Good luck...