This is the current location - I have tested the link and it is working.
http://lame.buanzo.com.ar/lame_enc.dll
Instructions from the Audacity wiki:
1. Download an unzipped copy of the required lame_enc.dll
here
2. Do not open this file, but save it to your computer. As you will be using this .dll file directly for encoding it is recommended to save it into your Audacity installation folder. This is normally at C:Program FilesAudacity. Once lame_enc.dll is saved to your computer:
3. Launch Audacity, click Edit > Preferences then the File Formats tab. Note: In Audacity 1.2.x, it may be necessary to click the left-pointing arrow top right of the window to reveal the tab. In Audacity 1.3.4 this tab is called Audio Files; in 1.3.5 or later Import / Export.
4. Look for the MP3 Export section.
5. Click on the "Find Library" button
6. In Audacity 1.2.6 this will ask if you want to locate the LAME encoder. Click "Yes". In Audacity 1.3.3 or later, click the "Browse" button
7. In the dialogue box, go to the folder where you put lame_enc.dll earlier, and select it.
8. Click Open, then OK.
In the same "MP3 Export Setup" section, you can then in Audacity 1.2.6 set the bit rate of the exported MP3 by clicking on the downward pointing arrow in the "Bit Rate" dropdown.