:welcome_s to DBSTalk, dm999!
At this point the only chance and it is a very small chance is to get a refurbished HR20 from DIRECTV directly and there is no guarantee that they will have any and that will be the unit sent to you.
Since you need OTA tuners you would need to go with the HR21's and the add on unit AM21 for the HR21's. Call DIRECTV and see if they will add the AM21's for free since you are upgrading from the HD TiVo.
At this point the only chance and it is a very small chance is to get a refurbished HR20 from DIRECTV directly and there is no guarantee that they will have any and that will be the unit sent to you.
Since you need OTA tuners you would need to go with the HR21's and the add on unit AM21 for the HR21's. Call DIRECTV and see if they will add the AM21's for free since you are upgrading from the HD TiVo.