There is the National QSL Bureau serving the Belarussian HAMs. The address is:
P.O.Box 469
Minsk 220050
Belarus.
Direct QSLs can be sent to addresses of Belarussian radioamateurs listed at the QRZ.COM site,as well as at the the sites of :
EW2EO - http://www.qsl.net/ew2eo/
EW4EW - http://www.qsl.net/ew4ew/