script to replace 3 fonts in multiple Excel SS's.

Our company has been using 3 fonts company wide for years that were owned by our parent company. Now that we have been sold we must discontinue the use of those fonts in all existing and future Office files. I've created a template in Word to remove these fonts but I am not sure about how to go about it in Excel. The three fonts that need removed are: "Tech Sans Black" "Tech Sans Medium" and "Tech Sans Book" and I can replace these with the Arial font. Any suggestions and help will be appreciated. I will be providing users with a macro that they can run against any spreadsheets that contain these fonts.