There's always eBay, but in my experience prices are always a bit too high, and then there's shipping.

One other consideration - I've purchased a few lots of miscellaneous software on floppies in recent years, and I've run into more than a few older floppies that are corrupted or degraded to the point where they can't be read.  Never quite know what you are getting until it arrives.

There's a lot of old software up for grabs out there via download - really the best bet.