The maximum rent limits for each county & family size which you found online are set by Dept of Social Protection.
Some areas of the country may set a lower maximum rent limit for a specific location or area within a county - for example it may not make sense for the same max rent limit to apply to Cork city and an area of rural Cork where rents may be a lot cheaper.
As local rent limits are set locally, they are not published online, so you should contact the CWO for the area to ask about them.
There is nothing to stop you making a new Rent Supplement application if you have previously been refused - however, the reason you were refused the first application may apply to the subsequent application as well (e.g. if the rent exceeded the max limit, or you didn't meet the renting/housing need criteria).