Some of my favorites
Truth Hair: https://marketplace.secondlife.com/p/TRUTH-HAIR-Gattina-Mesh-Hair-DEMO/4873823 https://marketplace.secondlife.com/p/TRUTH-HAIR-Tulip-Mesh-Hair-DEMO/6368730
For more hair, I'd recommend stopping by Elikatira, they have a lot of vintage, retro looking hair.
The Secret Store https://marketplace.secondlife.com/p/The-Secret-Store-Betty-Swing-Dress-DEMO/6281872 https://marketplace.secondlife.com/p/The-Secret-Store-Lady-Swing-Skirt-DEMO/3848874 https://marketplace.secondlife.com/p/The-Secret-Store-Lulu-Vintage-Dress-DEMO/5433389
They have a lot of items in the in-world store, and some aren't on the MP, so it's worth having a look. They came out with a new 50s, 60s bikini a while back that not on the MP yet.
SUGAR (not sure if most stuff would work, but the leather jacket might - quality of this store varies though) https://marketplace.secondlife.com/p/SUGAR-Zippered-Leather-Jacket-DEMO/6604998
I think you might also find some good clothes at Blueberry (tied blouses and jeans, mostly), Decoy (I know they have a vintage, 50s looking dress called Crisp dress) and Lapointe& Bastchild (jeans, leather jackets, boots).
Good luck