First thing that you need to clarify is whether you just want a Blackberry handset or the service as well?
Incase you just want the handset, get it from the open market, all sims for voice/sms service will work on them.
But the actual use of a Blackberry is with the service & only Ufone is providing it in prepaid.
Although I cant understand what you want but a Warid sim will work on a Blackberry set provided it is not locked.