Just went thru the same situation 2 months ago with some feral rescues and have done a lot of research on this topic. Unfortunately, kittens have very weak immunity systems and the odds are truly against your guy. An older cat that contracts FeLV has a higher chance of building an immunity to it. Both kittens that I rescued got terminally ill at 10 months old - most do not make it beyond a year and half.
Below is information that I received from Best Friends in Utah on placing a positive cat, and a great Cornell University Web site on the disease. I suggest that you read thru this carefully before you decide what to do. In the mean time, do NOT let this kitten interact with any of your cats. One of my adult, fully vaccinated cats did contract the disease from the kittens.
From Best Friends, on the topic of finding my adult FeLV a home:
Your best bet is going to be to place Ruby directly into a home yourself (rather than give him or her up to a shelter). The most likely options for placement are to try to find a home with another FeLV-positive kitty or a home with no other cats. You could try contacting local vets to see if they have clients with FeLV+ cats, or with experience with FeLV, who might be interested in adopting another cat.
For more advice on locating a new home, you might want to read our guide called "How to Find Homes for Homeless Pets." You can download this booklet from our website at:http://www.bestfriends.org/nmhp/prin...mesforpets.pdf
I would also recommend that you post the cat for adoption on the following websites:http://disabledpets.tripod.com/http://www.homestead.com/felinecompanions/http://www.petswithdisabilities.org/http://www.felinerescue.net/RESCUES_...CIAL_NEEDS.htmhttp://groups.yahoo.com/group/disabled-cats-rescue/http://groups.yahoo.com/group/Special_Needs_Rescue/http://www.disabledpets.com/
A few tips about advertising: It makes a huge difference to include a photo of your pet. Also, whenever possible, describe the traits, likes and dislikes, habits, and some of the little things that make Ruby special. Photos and descriptions really help people form a connection to an animal.
I'm also attaching a list of organizations that work with FIV/FeLV positive cats.
There is a lot of helpful information regarding the care of FeLV+ cats on the Internet. Cornell University has FeLV info at:http://web.vet.cornell.edu/public/fhc/felv.html
I wish you great success at your efforts. This will not be easy for you.