You might be tempted to search out vintage fabrics, but modern fabrics are more versatile. One of the best things about these newer fabrics is that many of them have a certain stretch factor. Any fabric with a hint of spandex will add extra comfort to a vintage pattern. Since most vintage patterns have little wearing ease, this can be welcome and sometimes even necessary. Look for cottons (for lighter garments) and wools (for heavier garments) with just a touch of spandex for ultimate comfort. You might also try polyester if you like the feel of that particular fabric. Polyester is especially suited to patterns from the 1950s and 1960s, but cotton is a perfect alternative. You might even try silk for more delicate patterns such as gown and blouses.
If you absolutely have to have vintage fabrics, you really should stick to the types of fabrics indicated on the pattern envelope. To find these vintage fabrics, check out eBay and Etsy. Sellers on both sites often have fabrics for sale. Bear in mind, however, that most vintage fabrics will be only 35" to 39" wide. This means you'll have to purchase a little more fabric than you're used to so you don't run short. A little extra is probably a good idea, especially since you might not be able to get that fabric again.
In most cases you can use modern fabrics. If you like a particular fabric and it's about the right weight, you can probably use it for your vintage project.