No 1099 due to under $10, how do I find Bank's FEIN to enter on 1099-INT? Turbo Tax won't let me leave it blank.

You might want to call the bank.  

For TurboTax online, in order to e-file, the IRS requires a valid employer identification number.  If you do not have one, you would have to print out your tax forms and submit them by mail.