Green Man Gaming is currently having an exclusive voucher for 23% off all items in their store which happens to include Fallout 4 and the season pass. This voucher expires on 10/09/15 so if you're interested you might want to take advantage of it quick. Also keep in mind that this is only for a code you can redeem through Steam so those with an Xbone or PS4 need to look elsewhere.
The voucher: 23PERC-AUTUMN-SAVING
Just apply it when checking out. If you you're not familiar with the site and think it might be a bit sketchy, don't use it. I've used them before but you never know.