Normally a reputable print shop can provide the ICC profile for you to use when soft proofing. You don't need to have an actual printer to do soft proofing. As long as you are using a color accurate monitor (measured with a colorimeter and using software that will generate a monitor profile to correct for any inaccuracies) you just apply the printer profile within your editing application and it will only send colors to your graphics adapter (video card) that the printer, ink, and paper in question can reproduce.

With the colorimeter and software you are generating an ICC profile for your monitor that makes sure (hopefully) that your monitor displays what your graphics programs tells it to display. With the ICC profile provided by the print shop or by the printer/ink/paper manufacturer(s) you are telling your editing application how to limit the colors it sends to your monitor. Both ICC profiles will be active at the same time at different links in the chain between your image image file and your monitor.

Having said that, though, it is usually a good idea to send a test image for printing before ordering a large, expensive print job from a printing house/printer/ink/paper combination you've never used before.