You could try one of these. The first one costs thou if you wanna crack a password longer than 2 letters... i dont know what the restriction is on the second one.
Try to use ARPR(Advanced Rar password recovery). I have 1.2 version, but I think that this version is too old nowadays. Globally, it is the best program to recover lost passwords for RAR archives(it's my opinion ;-). It includes dictionary attack, brute force attack...(however brute force attack is disabled in shareware version - you will need to download keygen ;-). Momentally, I don't remember where I downloaded this warez, but try search phrase "ARPR download" or "Advanced rar password recovery download" in Google. Some good sites are allways online...
P.S.: I try it and it works well(how a surprise for me P)