Does anyone know a good online shop to buy used pro microphones, such as Sennheiser shotguns or mics in that range? Thanks.

Try the consignment listing at www.trewaudio.com

There's a similar listing at www.coffeysound.com also.

I picked up a Senn. 416 on eBay, which required about $75 of repair work from Sennheiser--but it still was a fine deal, and a very solid performing mike. Obviously it's better to purchase from a reputable house like Coffey, but the prices reflect this.