An attorney in any city can represent you. I'm facing a medical inadmissibility issue, live in Vancouver but hired an attorney in Toronto as well. One reason to get someone with experience is that medical inadmissibility and excessive demand are significant issues in the Federal Court right now. For example, the link that someone else recommended was specific to a boy with a cochlear implant, and there is actually a rather significant case (from last year) dealing with a very similar situation.
The normal fairness letter will give you 60 days to respond. You can request an extension of time to respond, and it is likely that is what an attorney will do (it's the first thing my attorney did.)
The other thing to do is order your CAIPS/GSSM notes (there's a thread on this site if you search for "order CAIPS" but they won't let me post the link) first thing - they will tell you what the medical officer recorded as the reasons, although it may not say much at all, to be honest. Still, it is the best way to gain insight that's available to you.
When you respond, you can challenge the medical decision (in which case you want to have your own doctors opinions to send in) and/or you can provide evidence that you have a viable plan in place to provide for the social and/or medical services (this is a "mitigation plan".) The evaluation is also done relative to the province in which you plan on landing (in my case, British Columbia provides 100% coverage for the medication required to treat my "condition" which means that the medical officer ignored my mitigation plan, which was employer provided insurance that ALSO provides 100% coverage for the medication. In Ontario, that would not have been the case and it is likely that I would have been admitted.)
Only 0.22% of applications are rejected due to medical inadmissibility, yet they constitute a substantial portion of the non-refugee appeals cases. Even CIC admits that there are problems in the medical inadmissibility case (see the Auditor General's Report Fall 2011 - sorry, site won't let me post a link - where CIC admits as much.)
My own application was rejected (as medically inadmissible); my attorney was surprised at that ("I've been successful with far weaker cases than yours") and we're now in Federal Court (application for leave is now due by the end of February, 2012.)
Good luck!