Used to be just such packs, back when DSB's were all the rage...
Garf, Inland Aquatics, and a few others, used to sell Detritivore kits, came with bristle worms, along with many other sand dwelling critters:
Sadly, most of these companies are long gone. Garf is still there, but I don't think they've updated their website since Leroy passed in 2012.
Indo Pacific Sea Farms (ISPF) is about the only vendor left. Spaghetti worms, bristle worms, amphipods, micro stars... All kinds of cool critters. Pricy, though.
I'm not going to argue with folks about the desirability of bristle worms, amphipods, gammarus shrimp, micro brittle stars, asterina type stars... no reason for me to try. Lots of space in this world for folks that like 'em, and folks that will tear a tank apart trying to get rid of em.
To each their own.
Me? I like my reef as biologically diverse as I can get it. These days, it's hard to accomplish. A couple of samples from ISPF, a bit of sustainably harvested live rock and sand from the gulf, shipped wet... if I can get it. Getting harder and harder to find. Sand bed samples from healthy reefs in our local club used to be an excellent source... again, local clubs are fading away.