When I get material it's from department stores or I go have a look around markets nearby and buy from there. I've never had clothes custom made by another person, but have made a couple of garments myself.
However if you mean you are going to a dressmaker to get your clothes custom made then I would expect that it would be easier for them to get the material, they'll know the places etc and if you tell them what you want I'm sure they'd be able to find the most similar material (just a guess)
I for one would not order fabric online. I like to be able to examine the materials in person, and see if the quality is there, what the colors are really like, and if it is appropriate for what I want to make.
Fabric shops are all over the place and not hard to find, and you can get wonderful goods even from many of the cheaper ones.
Jo-Ann's and Hancock's are the major chains, and are actually very good, but I also like to shop from independent retailers. There's a local one here in Kansas City which deals principally with fine quality suitings and fabrics for formal wear.
If you are having clothes custom made, it is best to go shopping for fabric with your dressmaker if possible. That way you will be assured of getting the right materials for the jobs in the correct quantity.
i have ordered sample materials from a few places... much cheaper than buying heaps and finding its all wrong...
thanks as_you_like_it i may speak to some dress makers and see what materials they import.... i am trying to go for quality fabrics so that they will last years... but i heard chiffon can rip really easily when caught.
Chiffon is delicate, no matter where it comes from. It is a super-lightweight loosely woven fabric. Anything diaphanous, like chiffon, tulle (especially silken tulle) crepe, etc., are going to be more fragile than things like broadcloth, brocade, corduroy, etc. Among the lightweight fabrics, charmeuse and crepe wear pretty well where silks are concerned, and I am rather fond of cotton voile for summer wear. Another thing to consider are blends, especially the new microfibre synthetics, which can add greater wear and improve the "hand" of natural fibres with which they are mixed.
Satins may hold up well as far as integrity goes, but may lose their finish or get snagged, because their smooth, slick nature is created by having a dense layer of "floating" or unsecured weft threads which are subject to breakage or snags. Similarly, the smooth, mirrorlike finish of velvets will show wear as the nap gets crushed out of place or breaks down along seamlines. Any napped fabric will show wear along seamlines first, be it a gabardine, flannel, or even corduroy. Some fabrics actually look better when they wear in, however.
What sort of dress are you wanting to have made? Possibly I can give you some recommendations on what kind of fabric to look for.