Your 12.288 MHz is not strange at all. Similar common frequencies are 6.144 MHz and 18.432 MHz. If you use the 18.432 MHz and divide by 1.5 you can get to 12.288. Dividing by 1.5 is not too difficult to do (ie there are circuits to do it....which I normally put into a small CPLD). Another frequency to look for is 24.576 MHz which can be divided by 2 to get 12.288 MHz.

A web order electronics distributer here in the USA lists all these crystal frequencies as standard and available. Here is a link to one manufacturer's data sheet, that they handle, so that you see first hand as to what is standard:

http://rocky.digikey.com/WebLib/CT...Series.pdf

In the long run your easiest choice will be to just pickup a 12.288 MHz crystal from a shop in your location.

Michael Karas