They are variants of the model that came with the 7th Edition Skull Pass set which I believe are found in the current Dwarf Miners box (I'm not 100% sure as Saul won the sprues in a luck dip at the local GW a few years back).
I made some slight tweaks to the models to ensure they weren't all identical, the major addition being the inclusion of contents in the wagons. I dropped a small piece of plastic card in them and piled some wall filler on top before adding some sand and small rocks which I painted to represent unrefined gold ore (I have no idea what gold ore is supposed to look like so drybrushed black over gold which allowed for flecks of gold to shine out).
I love the little Goblin prisoner in the cage, a wonderful little touch amongst the plethora of extra odds and sods on the sprues. GW may do many things wrong these days, but sometimes they still get it right... :-)