I don’t shop much in grafton street but am somewhat familiar with the area. Here’s a few shops that may have maternity wear.
H & M, at the side of St. Stephen’s Green centre near Gaiety Theatre. Zara may also do some maternity clothes and this is beside H & M.
Next on Grafton may have a maternity section too. Oh and there is Topshop which is at the top of Grafton st (Shopping centre end). If you are facing the park with grafton st behind you, turn left and you’ll come across it.
In St. Stephen’s Green shopping centre you have Mothercare, Benetton and not sure about TK Maxx but thats upstairs in the centre.
Nelo is on Clarendon St. which is paralell to Grafton st. There might be other boutiques in the westbury mall and on South Anne Street. That’s all I can think of, hope it helps.