Hello Gary A;
I downloaded the updaters from Apple's site. Sometimes it takes a few searches to find what you need. Here's the quickest way to the updaters:
Click on the link on middle right hand side for Powerbook G3
You'll get a page with a listing of all 44 Powerbook updater links but you can narrow the search here, on the top right, by inserting the keyword "modem" into the existing search string thusly:
g3 powerbook modem kbdload
and click "search"; you'll get about 6 hits
Read the updater read-me's before installing them. These are the updaters I installed, in order, on my PB G3/233:
1) PB G3 Series Modem 1.0.2.smi
Easily installs a new extension; restarting allowed my modem to work fine; after restart go to Modem control panel (CDEV) and select port "internal modem" and modem script for internal modem then test dialup with Remote Access cdev
2) Apple Modem Updater 1.3.5.img
I didn't need to install this one because the firmware of the modem had already been updated. The installer figured this out. This installer also includes the above extension but you must manually install it.
3) Z-Apple Modem Updater.smi
contains a newer firmware updater. I installed this one also. make sure you read the instructions on these firmware updaters. Modem works fine.
If you are using your modem to access a network there are other updaters. To keep things simple, only install the updaters you think you need, and test the modem between updaters. If you're not getting a dialup after the first one, try the second one. I had OS 9.2.2 already installed and it didn't include the extension. I believe this extension will work for OS 8.1 and up, and possibly earlier. Good luck!