Jhb, the LNWR locos were brought over by the DW&WR.
'Accoiding to Clements and McMahon six former Webb 2-4-2Ts were sold to the Dublin, Wicklow & Wexford Railway in 1902. The price was £1550 per locomotive. Nos. 59-63 were returned to Britain in 1916-17. No. 64 was acquired by the GSR, but before that it had participated in the Civil War when it was armoured and named Faugh-a-ballagh.For a time it was used at the Mallow sugar beet factory and led a protracted existence as a boiler for washing outs at Inchicore. The locomotive had begun as a 2-4-0T in 1877 and was rebuilt as a 2-4-2T in 1896. '
Other LNWR stock was used on the Dundalk, Newry & Greenore, a wholly owned subsidiary in modern speak, of the LNWR. Some Wolverton built 6 wheelers were sold off the DN&GR and saw further service on the Cork & Bandon section in GSR days at least. I imagine the wagons were the same as the LNWR ones?
Also, the CB&SCR had a number of Beyer Peacock 0-6-0STs similar in design to those used on the LSWR. I think 1 or 2 of them made it into GSR times. Another oddball that made it into GSR stock and very early CIE days was former Allman's Distillery 0-4-0ST, a 'Beaufort' type Peckett a pretty much off the shelf product I think (apart from regauging)
Having said that, all the above are not RTR, I'd imagine you could get LNWR 6 wheelers in kit form.