Two essences come to mind...Honeysuckle & Walnut.
Honeysuckle remedies homesickness & difficulty in adjusting to new circumstances; restoring adjustment. It specifically sites for animals that keep being re-homed.
Walnut remedies difficulties in adapting to new circumstances and restores the ability to adapt to change. This essence references cats that are under distress w/behavioral disorders (aggression) associated with transitions in life such as new surroundings.
Both essences can be combined and are actually linked to one-and-other.
Can purchase from: http://www.mybachremedies.com/
or any decent Vitamin Store will carry essences...you can even purchase on Ebay.
For dosage, you take 2 drops of essence or essences and add to 1 fluid ounce of spring water -- this treatment bottle will stay fresh for about 3-weeks. Standard dose is 4 drops by way of mouth...directly on tongue if possible..if not, onto nose where it can be licked off...rubbed into lips, etc. If you can't get near the cat for mouth dosage, you can try a spray method and spray on body & surrounding area.
If you see no immediate change in behavior, you can continue dosage for up to 5 days. If nothing changes after 5 days...you can try another remedy.
Give it a shot...again, essences are completely safe for felines, they are inexpensive and proven to work.