We’ve been so lucky to live near several great shelters, now in two parts of the country. The SPCA in Charlottesville, VA where we started fostering in 2011 has a world of resources on their page that is helpful to locals and non-locals alike. They even have a link to a Foster Kitten Handbook that is 23 pages long!
Check out the Charlottesville-Albemarle SPCA site on becoming a foster.
Here in Reno the Nevada Human Society has a very active fostering Facebook Group. It’s a very fun community to be part of.