One of my faves for buying silk is, Preview Textiles. From silk linings like China Silk, Charmuese and Organza's to Silk crepes, Satin Back Crepe, and Satin Faced Organza's, and more, in over 50 shades (and a couple of them are grey).
There are no minimums, and anyone can open account, BUT, this is not like a fabric store where you can roam around pulling out rolls of fabric.
If you are a first timer at Preview, when you enter you will be asked, "How may I help you?" or "What company are you from?". These questions can throw newbies off. You can be you, whether it's a small unknown company or a grandmother making a wedding dress, just state your name and what kind of fabric (silk satin, crepe, chiffon etc). There are no polyesters, interfacings, or laces. The office manager will either show you a color card, direct you to the closet for swatches, and/or the wall of fabric samples. When you make a choice, give the Office Manager your order (you may need to open an account, but no big whoop), give her your fabric type, color number and amount of yardage. You can pay via, credit, debit, and even cash (l least recommend cash, it becomes a pain to get change). You get your fabric in minutes, on a roll or folded.
Easy and you can buy silk fabric from the same place as the big companies.
225 West 37th Street 11th Floor
New York, New York 10018