Hello! Welcome to iFixit! Thanks for asking your question. You can purchase iPad 5th generation home buttons online on popular stores like eBay.
Here is a popular home button replacement: https://www.ebay.com/itm/193384176556?hash=item2d06985bac:g:r2oAAOSwa~JbRhL8
This iFixit guide can help you replace the home button: [guide|88325]
Hopefully this has been helpful to you. Have a great rest of your week. Thank you for using iFixit!