Theoretically you could deduct the cost of the keyboard as a job-related expense. However, job-related expenses are a miscellaneous itemized deduction subject to the 2% of AGI limitation. That means that 2% of your Adjusted Gross Income (AGI) is subtracted from your total miscellaneous itemized deductions. Only the remaining amount is deductible. In addition, the deduction will not have any tax benefit unless your total itemized deductions are more than your standard deduction. So you will probably end up with no actual deduction.
As an aside, you should look into whether the law requires your employer to provide the type of keyboard that you need. It's my understanding that employers are required to provide a "reasonable accommodation." It might be under the Occupational Safety and Health Act (OSHA) or the Americans with Disabilities Act (ADA) or some other law. But this has nothing to do with taxes, so you will not find the information here in TurboTax AnswerXchange. You will have to look elsewhere, or ask a lawyer who specializes in employment law.
