Why do you want to use stainless steel for the bearing balls? If you're using standard linear rail it's still made from En31/52100 or similar material and can corrode. 440C balls are a good choice if you need stainless properties, be sure to use Grade 25, lower precision grades may not give the accuracy or wear life you want.
5/32" 440C Gr25 balls are available from many USA suppliers, a quick web search will find them. Be sure they will ship overseas.