John,
In the National BGR rules the 'Howdah' pistol event isn't classed as one of the 'core' events - but it can be run by some branches as a supplementary event- Refer page 26.
https://ssaa.org.au/assets/disciplines/BGR-National-Rules-No.4-2016.pdf

17.1.15 Howdah Pistol
a. Minimum calibre .375
b. Single or double barrel
c. Smooth or ball rifling
d. Minimum muzzle energy 1,000 ft lbs
e. Minimum 300 grain bullet weight
FIRING SEQUENCE
Howdah Pistol (max. 10 shots)
 25yds – to be decided by Host Branch
 10yds – to be decided by Host Branch
(“Tiger” target if possible)

I've only heard of them & only 'seen' the ones displayed here in NE, perhaps contacting BGR national might be able to put you in contact with someone who has one?
https://ssaavic.com.au/disciplines/big-game-rifle/

They are a great bunch to deal with, always helpful with reloading tips & tricks to keep these old timers & 'oddities' up & running well
Hope this helps
93x64mm