On Amazon, these items can be purchased with most FSAs (Flexible Spending Accounts) and HSAs (Health Savings Accounts). If you have a card, you can add it in checkout. You can also purchase these items using a different payment method and choose to be reimbursed from your benefit administrator later.
https://www.amazon.com/iWALK2-0-Hands-Free-Knee-Crutch/dp/B00092RB06