Hi, and welcome to this group. I just wanted to ask if you are on Facebook at all, because it seems to me that a number of the active rescues (and breeders) are using that type of social media to advertise their available rescues (and new litters).
We have a yorkipoo, a shorkie (shih-tzu/yorkie) and a Biewer. Love them all, would recommend any of them to potential owners - the yorkipoo and shorkie are rescues and the Biewer we got from a local (PA) breeder.
Here's one FB page link that is used for Adult yorkies to be rehomed:
https://www.facebook.com/groups/245780945575969/
Hopefully someone else who is involved in rescues and is on this group will respond with more info and recommendations for you. Best of luck!