Indeed. The Regency shako appeared in 1816, although the short, Napoleonic jacket soldiered on into the early 1820s. You can see them being worn as late as the First Anglo-Burmese War. That said, a combination of plastic British Napoleonics with donor shakos from Russians or maybe French Hussars.
The Foundry Afghan range could be worked up but it would require some work as they are all in shell jackets, which weren't typically worn outside of the warmer garrisons. The Empress chaps in temperate uniforms are wearing the later, long tailed coats.
The Perry Carlist War British Legion probably offer the simplest route. You would need to paint lace on the coats and maybe file back/ alter the shako plate.
If your scenario is set in the colder months then the Empress range has some great, animated, figures in greatcoats from the retreat from Kabul. The greatcoat was essentially the same for the entire period.
It all depends on how hung up on detail you are. I have the Empress British infantry both greatcoated and in coats for the 1830s as well as the Perry Royal marines and would quite happily use them from the Radical War (1820) through to the First Afghan War and even a little beyond). Come to think of it I still have the old Foundry Afghan/ China war infantry knocking about.