Roger;

In the interest of presenting all solutions, several other variants should be listed, including those which don't involve changing the original Fuseblock:

1. Simple replacement of the fuse! These are available!*
2. Harvesting the 25A element from a more common 7 X 25mm (GBC) and simply installing it on the 7 X 17mm ceramic carrier (not absolutely stock or pretty, but technically perfectly adequate and reliable!).
3. Paralleling Fuse 1 terminals with a modern Fuseholder with a 25A fuse installed (this is the recommended immediate fix to keep a vehicle roadworthy while organizing a replacement).

* Planetman has stated he stocks these, and I do as well.

While your at your Fuseblock, check for excessive greenstuff! Suggested reading: http://www.sw-em.com/gastight.htm

Cheers