I was right.
Foundry has one:
Here is the link:
http://www.wargamesfoundry.com/collections/INDIA/6/index.asp(it is in their Indian range.)
Although a little early for the period you ask, I think it is a simple conversion, by adding the proper limber and gun!
Ah, and you can use the elephant with howdah in the same page as an alternative trop carrier.
BTW, since I have a (slight) idea on where you will use it, please [although I am not in any way an expert in animal physiology] note:
.- elephants are very slow walking. Oxen driven artillery/wagons might match their speed. So, a man on foot can accompany them at ease step.
.- elephants are tropical beasts and like warm weather. I believe that they cannot easily survive at the cold and high altitudes and thin air of The High Pamirs. And they need lots of fodder! Yes hannibal crossed the Alps with elephants, but I think with great loss.
The heights that Hannibal crossed the Alps are much lower than any of the Pamirs!
[see also the link abot Hannibal crossing the Alps:
http://www.livius.org/ha-hd/hannibal/alps.html ]
maybe mule driven artillery (the Indian army mountain gun by brigade games might be a better choice?

?)
Or change the animals: use bactrian camels or Yaks!!! (convert the bactrian camels or yaks produced by Copplestone or Irregular miniatures to carry your Indian Army mountain gun.)!