Maybe that negation would be too obviously related to the idiom. There are other ways to say there is a way; e.g. instead of shikata, there is houhou: 方法 (方法がある).
The counter-idiom, if you will, to "nothing can be done" might be "where there is a will, there is a way":
意志のあるところには方法がある。
If someone says しょうがない or しかたがない, and you don't agree, that might be the thing.
Grammatically, its negation would be "Shikata ga aru", but I never heard this said once.