I’ve added some links to download the collection of ArcView 3.x extensions. I can not elaborate in more detail about these extensions because quite a lot of numbers, but some of them may be very useful for you.

However, some extensions that I provided here is a setup program, so
you have to install it. Extensions ArcView 3.x that requires the installation are  Spatial Analyst, 3D Analyst, Network Analyst & Image Analyst.

ArcView 3.x Extensions (5 mb) | Spatial Analyst (24 mb)| 3D Analyst (12 mb) | Network Analyst (1 mb)| Image Analyst (94mb) |