This is extremely difficult information to obtain since CLEOs don't want this information advertised. Your best bet is to setup a meeting with your CLEO (or a town that you are interested in moving to) and have a frank discussion. Tell him you are a collector, you will have everything locked in a safe, won't be shooting it and that you are responsible, etc. Ask him what he thinks, what he would like you to do to make him comfortable with a signoff.
I've only had experience in two towns, Westboro and Holden. Both Chief's were very accomodating and Sherrill from Holden went out of his way to help me. In both instances, I setup hour long discussions to talk about the subject, before I went in for my signature. I believe this, getting dressed up and looking responsible will help.
Town info based on friends:
Shrewsbury: no way.
Worcester: a handful have been given, but you need to have help / know someone
Northboro: possible, although Chief requires an alarm system that is monitored and will notifiy police if there is a break in so you will have to invest some $$
Sterling & Rutland: yes, I have friends that were approved
Watham: I was told no way, but I know some people that got green cards (ex Pats football player that you may have heard of....
)
The farther west you go, the higher the liklihood of success.