Not to rain on your parade but as Brendan said, this is not the best enviornonment to commence such a business. Bear in mind also that while designer brands have appeal to the younger ( and sometimes not so young ) clientele, what is the position now and in the next couple of years expected to be vis a vis disposable income amoung the younger generation? Also, in relation to footwear, while margins are generally good ,sale times and discounted and end of- lines can mean effective margins well below the apparent full price margin. If you do not have any direct experience in footwear, then you need someone very good and experienced on board or you need to gain that experience.
Specifically on wholesalers, if you google "footwear wholesalers" Ireland, you will get a list of some. Also a lot of the brands you mentioned will likely come through UK or continental agents. A bit of research here on brands, margins etc. could be a good start.
Something else, a new phenomenon among the younger buyers is to go into a shop selling the brand you like, check it out get the size right then buy online. It's happening quite a lot.