I don't know of any; I think the fun in making something like a Westinghouse pump in this scale is to make it all yourself from individual bits! If it's to be a dummy, then you can soft-solder carefully-machined chunks of brass together to create "castings". There's not a huge amount of cast-in detail on a Westinghouse pump that you can't fairly easily create in this way. (The top valve housing would be fiddly but not impossible.)

You could even use aluminium and Araldite, as your pump's on the cab and not the smokebox, so it won't get too hot.

Work from photographs and sketch out the bits, resolved into machinable blocks. Lots of pix on the Interweb thingy!

The pump on my Isle of Wight O2 is a working one, (steam/water, not steam/air) but it only looks vaguely like the real pump as it's just too impractical to make it work in this size. (Somebody will prove me wrong…)

To get the detail in a Westinghouse pump casting, it would really need to be a lost wax affair and that would make it expensive.