You can start by having your Realtor research listings to see if any have gas. In many cases an experienced agent can tell you by neighborhood what services are available. If gas is available in the area I would think the next step would be to contact the local utility complany to determine where the closest service is and then contact a reputable plumber to get a cost on bringing it in to the house.... more
Hi Mary - Even if the home is sold 'as-is', you still want to have the entire home inspected. Since this type of system is uncommon, and more complicated that standard forced-air systems that are in 95%+ of the homes out there, you would be well served to have a heating technician with specialized experience with this type of system. So, you would have this guy look specifically at the system in addition to a general home inspector.
I wouldn't necessarily rule out the home because it has this type of system. If it's in good working condition, then you may really enjoy this type of heating. On the other hand, if it's in poor condition, the cost to repair could be a lot more expensive. And retrofitting older houses to accommodate a common forced-air system (with an air handler, furnace/heatpump and ductwork) can be prohibitively expensive.