The online store where I have gotten most of my stuff has been from
http://allheart.com/ They seem to have a really good selection of products and at good prices. The stethoscope that I have is a Littman Master Classic II and I'm really happy with it, but I don't have any experience working in an ER to test it out there, though it seems to block out a lot of outside noise. I'll keep you posted if I hear of any good stores in the city.