Hello
If you need more information on Rage Syndrome in Cockers, then have a look
here Hopefully this site will answer all the questions you may have. Rage is thankfully quite rare but you do see poor temperaments occasionally in all the colours, mainly due to poor breeding practices & lack of socialisation, especially in puppies bought from multi-breed commercial kennels. If you buy a puppy from a reputable breeder, then you should not have any problems with temperament, although of course, temperament is also to some extent dependant on continuing socialisation & training by the new owner.
I'm afraid you will find it very difficult to locate a solid chocolate Cocker pup if you are looking for the type of Cocker you see in books & on most websites ie the show-type as this is quite a rare colour nowadays. I understand the colour is more common in Working Cocker lines, but Working Cockers do look somewhat different to how you probably imagine a Cocker to look like & need plenty of mental stimulation, being very busy, active little dogs. You would probably have more luck locating a reputable breeder if you were able to be more flexible on the colours you would consider
HTH
Jane