Hi,
The Durham Children's Aid Society in Oshawa was open at that time and catered to a large part of durham (next closest I believe is the Peterborough CAS). I was adopted from Durham CAS in 1971 and they are still open now.
www.durhamcas.ca.
If you have not already done so, you (might have to be your husband) can contact them for non-identifying info. I did this and was provided with 2 pages worth of details on birthparents, birth families, the birth itself, etc. Although no names are included, this info is still great. Soon you will also be able to apply to the government to get your husband's birth name and his birth parent's names (as long as they have not opted out). I believe this in effect at some point in 2009.
If it was a private adoption, I'm not sure. Hope this helps!