There aren’t a lot of standard editions of her work out there, and since so many of her works were originally published in the pulps, many are paperback reprints from the 60s & 70s. Ace published a number of her best stuff, though under different name from how they appeared in the pulps. (For instance, Shadow Over Mars is reprinted as “Nemesis from Terra” and The Starmen has been reprinted as both “The Starmen of Llyrdis” and “The Galactic Breed”). While Sword of Rhiannon is nominally anthologized in Brian Aldiss’ “Space Opera”, it’s just the opening chapter, but the paperback with the full story is fairly common in several editions.

All of the titles I’ve mentioned, plus “The Halfling and Other Stories”, I’ve seen around in paperback, though you may have to hit some top notch flea markets or indie used book stores to get them, unless you just want to look for them on Amazon.

Haffner Press has put out several prestige anthologies of Brackett’s short fiction, but these are very expensive and hard to find.