This site is reported to offer a wealth of economic information on Turkey. However, the slow connection the two times I tried (including Saturday morning) made it rather difficult to use. Perhaps a network upgrade will soon increase the speed.
The interface is telnet. Each time you use the system, use the
logon of "tcmb". The first time you will be asked for some information,
and then given a user code. It should be used for subsequent visits
(again, given after logging on with "tcmb").
telnet://tcmb:tcmb580.tcmb.gov.tr