Are you willing to pay for this service, or are you trying to get it done on the cheap (free)?
SGS Ludwig on Ogden Road SE does atomic emission spectrometry, that will provide a very accurate analysis, but it won't be free. Budget around $200 per sample.
A scrap yard, third party inspection firm, or a welding shop that does a lot of stainless or alloys, will often have a portable X-ray fluoresence machine. These things are super easy to use and cheap to operate, so if you have a friend there they may provide analyses for free. Accuracy is okay enough for the purpose.