I bet it's hard to find a fosterer for a senior cat, regardless of how sweet he is.
I trapped a litter of feral kittens and their mom and brought them to a local foster/adoption/spay neuter group. Unfortunately, I wasn't able to trap them until they were almost ten weeks old, and one of the cats went through two fosterers without making progress. They ended up returning him to me, neutered, about a month ago. He's outdoors--we're at our indoor limit--but I have a small stray/feral colony I feed and trap/neuter/release (and sometimes find homes for). But I was surprised to see him bond with one of the stray adults. Then I was even more surprised when he started letting me pet him when I pet his buddy! Now he approaches me, circles my ankles, and purrs.
So if Sarai doesn't have FIV or leukemia, and if she's still fairly young, maybe another fosterer could make it work if Sarai gets attached to another friendly cat. Meanwhile, I hope you have a wonderful--and easier--time fostering Paco. If you go that route, please share photos!