I looked into this for a recent trip and it seemed impractical except during summer months. Check:
http://www.gov.nf.ca/tourism/ I can't remember where I found the ferry info, but I recall that outside of summer the only hope is milk runs that stop everywhere and take a week or more.
For the ferries to/from NS:
http://www.marine-atlantic.ca/marinee/wheel/index.htm
Allow three weeks to see Nfld island. It's a big place and all very worthwhile, IMHO.
I intend to post a trip report shortly.