Etsy.com actually has quite a bit of stuff since it is user-curated.
1stdibs is AMAZING but they are very pricey because they only offer stuff that is considered more collectible. Some amazing pieces though.
There are a few other random stores you may find by searching specific designers, manufacturers, or series names from the time period you are looking for.
As always, the most economical option is to scour your local craigslist, goodwill, salvation army, flea market, etc. on a regular basis. Obviously this involves more waiting and luck but my wife and I have found some fantastic pieces this way.