Here are modems, cables, AppleTalk and LocalTalk networking adapters and cables as well as manuals and communication software.

Modems vary from 300 bps or baud to 56K.

Popular wisdom varies, Serial cards on the Apple II’s max out at 9,600 or 19,200 baud. Early Macintosh’s to the 68030 processor, or so, also max at 9,600 or 19,200. The IIGS has been reported to reach 56K although the highest speed is officially 19,200. Please research for your particular computer.