Although there are homemade recipes for creating fire retardant
liquids, the best source(in this day and age of liability) is to look
on the net for Theatrical Supply Companies. Many stage items have to
be sprayed with fire retardant chemicals. It has been awhile since I
looked at these companies, but my recollection was that they were not
very expensive and could be bought in relatively small quantities.
The reason I seached for these companies is that some shows require
that the fabric used for displays or covering tables be treated. I
hope this helps.