There should be no VAT charged on an export from the UK, import VAT will be charged at that countries full rate on the import.There is a free trade agreement between UK and EU, so there is no customs duty to be paid when you import from UK, including from NI.
You will however have to pay VAT, in UK side, plus the differential between VAT rates between UK and ROI. If say VAT in UK in that product is 15% you will be charged that by the UK supplier. If the VAT is 20% in ROI, you will pay the difference (5%) in ROI.
Any chance Morris have an agent in NI? If they have, that would be the most convenient way for you to get your hands on it.