What has worked fairly well in the past is made with a base of rotted fish. I usually use suckers for this. Just place the whole fish in some glass jars, put a lid on the jar and set the whole thing out in the sun for the summer. It will turn to liquid after awhile. Then add some anise oil, fresh beaver castor, catnip, glycerin (to keep it from freezing) and bobcat urine if you have it. Otherwise, you can leave it out. Some skunk essence also works pretty well.
If you don't want to go to all that trouble, you can order scent from several different companies. O'Gorman, Hawbaker, etc.
By the way, what type of e-call do you have? I hear a yellowhammer woodpecker in distress call works good for cats but have not had much luck with it myself. Only cat I have called in was with my Sceery AP-6 hand call.
Good luck with the cats, hope you get one.