Unfortunetly we have found over the years the more we advertise, it's not volunteers or foster families we get but for each ad up to 10 people wanting us to TAKE their animal
And well we just don't have the space, nor the man-power.
So, I think the majority at the moment is word of mouth. I am not the Shelter Coordinator, so i am not sure what all else they do looking/asking for volunteers.
I know I mention it at events to people stopping by our booths, any rabbit lover I may meet anywhere, and posting on like facebook and such. I am sure my friends are done with me asking for help LOL
We used to advertise in the local papers and even on Craigslist, we also had posters and such in Vet clinics. I honestly don't know a animal rescue organization that would turn down some help
There's just not enough people to go around it seems. But i would check those areas, and a search online of who's near you and contact them.