form 8283

It's unfortunate. You must continue to solicit a manager at your Goodwill location.  I would advise requesting them to call on your behalf while you are at the store.  This is not unfamiliar territory for Goodwill.   This signature must accompany your form when you complete Part I Section B. Without this form the IRS may deny your deduction. 

Notes:

If you are electronically filing your tax return, you must include the Form 8283 data in the electronic submission. Enter all information requested by a line of the Form 8283 on the electronic Form 8283, except for the required signatures.

Caution:

You must attach the completed Form 8283 with all the required signatures to your tax return, either as a PDF attachment when electronically filed, or mailed to the IRS with Form 8453.

If you are a member of a pass-through entity and are filing your tax return electronically, you must file your own Form 8283 electronically while attaching the pass-through’s Form 8283 as a PDF attachment to your return. A member’s Form 8283 is not required to have signatures in Part III, Part IV, and Part V of the Form.