I have only heard of cranberries as a possible help. Fresh cranberry season starts in October.http://whfoods.org/genpage.php?tname=foodspice&dbid=145
"Prevention of Kidney Stone Formation
Cranberries contain quinic acid, an acidic compound that is unusual in that it is not broken down in the body but is excreted unchanged in the urine. The presence of quinic acid causes the urine to become just slightly acidic-a level of acidity that is, however, sufficient to prevent calcium and phosphate ions from joining to form insoluble stones. In patients who have had recurrent kidney stones, cranberry juice has been shown to reduce the amount of ionized calcium in their urine by more than 50%-a highly protective effect since in the U.S., 75-85% of kidney stones are composed of calcium salts.
In one recent study evaluating the effect of cranberry juice on kidney stone formation, study subjects were divided into two groups, one of which drank 2 cups of cranberry juice diluted with 6 cups water each day for 2 weeks, while the other group drank tap water for the same period. After a 2 week period in which neither group drank any cranberry juice, the groups were switched, so that those who had drunk cranberry juice drank only tap water, while those who had drunk tap water consumed 2 cups cranberry juice diluted with 6 cups tap water daily for an additional 2 weeks. In both groups, drinking cranberry juice was found to significantly and uniquely alter three key urinary risk factors for the better: oxalate and phosphate excretion decreased; citrate excretion increased; and the relative supersaturation of calcium oxalate was significantly lower.
In another trial that evaluated the influence of cranberry, plum and blackcurrant juice on urinary stone risk factors, cranberry juice decreased the urinary pH (made the urine more acidic), and increased the excretion of oxalic acid and the relative supersaturation for uric acid. The researchers concluded that cranberry juice could be useful in the treatment of brushite (calcium) and struvite (non-calcium) stones as well as urinary tract infection."