Changi

egnite Software GmbH has the old Changi source. I contacted them about it and received the following reply 8 May:

Hello Mike,

Mid last year I sent the sources to Paul Ratcliffe and I think he already modified it. You may contact him at
http://home.clara.net/orac/os2.htm
paul@orac.clara.co.uk

Best regards,

Harald Kipp

I haven't heard back from Ratcliffe as of 10 May.

New - old book

Found and bought Steve Mastrianni's "Writing OS/2 2.1 Device Drivers in C" on Amazon. Old but cheap... Also, his website has some stuff..