In the recent issue of Yorkshire Terriers magazine Popular Dogs Series by Dog Fancy Magazine (vol. 16)...there is an article on therapy dogs.
"Several national, regional and local organizatons certify therapy dogs. You can contact one of these (listed below) or a local obedience trainer may be able to help you find a therapy- animal organization in your area"
The Delta Society -
www.deltasociety.org
Love on a Leash -
www.loveonaleash.org
Space Coast Therapy Dogs -
www.spacecoasttherapydogs.org
Therapy Dogs International -
www.tdi-dog.org
Therapy Pet Pals of Texas -
http://therapypetpals.org
"if you're interested in doing therapy work with your Yorkie, it is best to go on a visit with another dog and handler team just to see what's involved and how much the dogs enjoy the attention they get"
"Your Yorkie is a therapy dog candidate if it has the following characteristics: an outgoing personality, basic obedience skills, gets along well with other breeds and people of all ages, is atleast one year old and has current vaccinations, and is free of internal and external parasites"
Certification requirements vary.
As an example, Therapy Pet Pals of Texas (TPPT) takes dogs and handlers through a certification class and a temperament test (for the dogs). If you pass those, you make a minimum of three training visits at the facility you choose to visit. You must go through this process even if you have worked previously with therapy dogs.
Check out these websites and see what their certification requirements consists of and see if there is anything in your area.