H i Anita:
This is what I found for Joshua Hatfield.(listed below). If this is your Joshua, you may order a copy of that application by sending a check of $10.00 payable to The Treasurer General and send it along with his info to:
The Registrar General NSDAR
Attn: Records Departmant
1776 D Street NW
Washington DC 20006-5392
This is a busy department so be patient, it has been taking 6-8 weeks for a reply.
We will try again to have someone contact you. Send your Name, Address & phone number to our supervisor Glenda at this e-mail address GlendaMT@aol.com
She can put you in touch with a chapter.
If you Grandfather was still alive in 1930 you should be able to order a death certificate. Since you know when your grandmother died you at least have a time frame from 1930 until the year of her death.The death certificate would most likely have his birth date on it. I think that is what you should aim for.
A census record would work. If I were you I would find the census that has your grandfather with his parents. You didn't say which line you are going through to join the DAR.
Good look on your research.
Laura
this is a free lookup service provided by the DAR VIS Volunteers at this message board

HATFIELD, Joshua
Birth: NY 6 Aug 1746
Service: NY
Rank: Capt
Death: NY 8 Aug 1820
Patriot Pensioned: No Widow Pensioned: No
Children Pensioned: No Heirs Pensioned: No
Spouse: Sarah Oakley
Spouse: Hannah Oakley
Spouse: Martha Loder