Hello the4hersclub! ;)
To find movie set/production companies' addresses, you can visit
http://www.imdb.com to see where's the filming locations and who's the production company. Then you can Google that information to see if it leads you to an address. If you cannot find an address or if you are unsure if it's correct, then you can go to the "Request a Via Venue address" forum here on Fanmail.biz. ;) The moderators will give you an address within the next few days!
A few tips when writing via venue:
- Don't send your letter too early (weeks before filming starts) or you might get a RTS.
- Make sure to send a photo to be siged and a stamped envelope with your address on it along with your letter. Actors usually do not have stamps and photos with them when they're filming.
Good luck!!

If you have any more questions, feel free to ask!
Regards,
Lizanne