They get some by trading stars before they reach 2nd or 3rd year arbs.
Back when Certificates of Deposit were a big thing, I remember buying $5,000 in a CD every month and put them on auto roll-over. That way, every month, if I needed it, I'd have one maturing with interest. This is how the Rays do it, in part. They buy a CD (trade a star) and wait for it to mature, but when you do it every month (year in baseball), you end up having one maturing everytime you buy (trade) one.
Of course, they are near the top in pitcher development and scouting other team's fringe or journeymen players that are nearing their career years or are a teak away from having a 2-3 year stretch of plus ball-playing.
None of this goes against a big spending team's goals and priorities, but it takes discipline and an understanding fanbase that won't boycott the team after trading a star. You have to begin that cycle somewhere, and the getting started part is the hardest. This past deadline was the perfect chance to start that ball rolling, and Bloom either chickened out or was told not to trade any stars or semi-stars, but Vaz.