I've reviewed the accessibility map (aimed at those requiring wheelchair access) and had a moment to think about how to best answer your question about reduced mobility access to the Paris Metro and RER.
I think the best way to discover which stations have minimal walking requirements is to use the Metro route planner tool
provided by the Paris transit authority. You won't be able to inspect each station for its stair climbing requirements, but you will be able to find walking time between connections. Based on the number of minutes required to make a connection between Metro/RER lines within a certain station we can estimate the difficulty of the transfer on mobility impaired travelers. When using the route planner tool, be sure to select "Shortest walking distance" under Advanced Criteria.
I don't have a list of stations which have significant stair climbing requirements as there are simply too many to mention (297 stations and 381 connections for the Metro alone). One thing to keep in mind is that some larger stations have multiple paths to descend onto the same train platform of which some of will be stairs only and some will have escalators/elevators. If at first you arrive at a stair only exit you could try further down the platform in search of an exit serviced by an escalator. For example, at Chatelet Les Halles station, RER A trains stop at very large, long platforms for which there are two sets of stairs and two sets of escalators spread out across the platform. If at first you don't arrive at a escalator serviced exit, keep walking or follow the overhead signs to find a set of escalators.
Nearly all stations and all connections have escalators along side stairs that are significantly long (roughly 25 steps or more). This doesn't mean that all of them will be working as breakdowns are pretty common and there's a shortage of technicians for elevator and escalator machinery in Paris.
Hope this helps,