I do think that Gluesister understands where you are coming from.
I would politely refuse, something vague like
"I'm sorry but its not possible for me to do this now"
You don't want to get drawn into discussions about why you can't do it. Only you need to know if its not possible because you don't want to do it or not possible because of practical / logistical issues.
p.s.If you do decide to help shall I start looking for Sylvanian family toys on ebay 