TIEpilot.
I see that you are new here, so welcome to the site.
that being said... there are other sections of this forum where casting, trading, and selling of items is handled. This is a section for people to post finished products of their customs.
I suggest that you do some digging on your own, in those sections, and find out who has what available already.
I personally don't think anyone has tried casting the guns for any of the at-st vehicles. I believe the only vehicle weapons that anyone here has actually cast are the firing missiles from the LAAT gunship (and that was done by clonehead, again, this is listed in his thread in the sales section of the forum).
Personally, my suggestion would be to look through e-bay for any partial walkers that people may be selling on the cheap. Or to look for that particular part itself. I know alot of people tossed or traded the larger missile firing chin-gun because it was not as screen accurate.
The thing about making resin molds is that it's expensive. Making a mold of that large a part would take a large amount of material. It would be much more cost effective to just try and find the part from an existing walker that someone doesn't want. Again, you can make that request in the sales, trades, wants/needs sections of the forums.
I would also suggest you find a reference picture to show exactly what your wanting it, and give a better explanation of what your going to do with it. everyone here is very willing to offer ideas and solutions to problems... someone might think of something you havn't.
good luck
