Admiral:
As you can see here, currently in the upper row of pictures, the Perry twins have some future releases of metal ox wagons planned, obviously intended for armies’ bagage trains. Whilst I’m unsure about the size visavi 28mm heroic scale Dwarfs, I believe the oxen might make for some good Bull Centaur bodies, whilst the ox heads are useful for statues, war machine decorations or the like.
If the size prove right for Bull Centaur conversions, the soundest thing to do would be to strike an agreement with a friend collecting a Fantasy human army in order to get the oxen whilst the wagon and handler accrue to the human player, just needing a pair of WHFB horses and maybe some army-specific details to fit in with their collection. By splitting up the purchase in this way you might get some decently cheap bull bodies.