I have recently bought an Anycom PCMCIA sized bluetooth card from ebay for £3.99 Sterling, which works with my handheld, a Casio BE-300 Pocket Manager
(with CF - PCMCIA Adapter jacket
) and MIPS processor Windows CE 3.0.
http://rover.ebay.com/rover/0/e11401.m516.l1123/7?euid=a7fd06163065...
Scroll down the page to see more units that are available. I needed to download the drivers from the Anycom website but installing was no problem. Just thought this might help.