Low residue food?

[rattastic725]

Our foster cat Julie had coccidia and was treated with aldon.  She tested negative this week but her stool is still slightly soft.  The vet said she needs to go on a low residue/resin cat food to see if that firm up her stool.  Julie is currently our foster to adopt and we really want everything to work out and for her to be healthy.  Does anyone know of a low residue food that is over the counter.  I know the vet has some but I just wanted to check.  Also, is it okay for my cat, Luna, to eat the special food?  The foster coordinator is really good about helping me out and is going to get food from the vet.  I was just researching our options!

Thanks in advance!