it seems many clubs are closed during summer. Here's a website that lists some:
http://www.jazz-clubs-worldwide.com/docs/holland.htm
I haven't been on record shopping tour in Amsterdam for ages, I doubt I could even find anything back. Big rekkid shop: http://www.concerto.nu/
other one (be warned that the people who work there, see it as work, not as a hobby): http://www.plaatboef.com/pltbfmain.html
I know there's a good one near the Rijksmuseum, but cannot tell you where exactly. Here's a list to be investigated at your own risk. I found more online, but most is in dutch.
Good luck and have fun, and don't have your bike stolen!