Certain activities drop rocks more frequently, I think... If your in search of rocks specifically, I would follow Sy_Accursed memory and switch skills then come back to Hunting normally. But if Hunter is your last skill to find a rock in...well... just hang in there :P
Obviously your concentrating on melee/slayer. Either continue with that or... As suggested above, herb runs. Cutting Yew Logs is okay. If you combine cutting Yews inbetween Herb runs, its an okay start. Cutting yews earnt me enough to by santa... back in the day... when it was 20m... now its almost 200m! :D