Cavalry

There is an Ironairsoft SMLE, which is very close in action to the real thing. It even field strips like the real gun. It is however a royal PITA. It takes some work to get it to shoot and my magazine blew up after I had achieved this (potentially quite dangerous). Still a great gun though when it works. Ironairsoft can be contacted via facebook and I am informed they will be making their next batch in May (I asked when I would be able to get a replacement magazine).
If you want something reliable and accurate, a spring version would be better. Check out Shootandscoot.co.uk

If you use airsoft guns, you may want to consider eye protection for both the riders and horses. Airsoft guns shoot small plastic balls and are more likely to ricochet back and hit the shooter than a bullet is.

This sounds ace, I'd love to be involved with something like that. Have you considered sub-12 ft/lb air rifles? For serious shooting and marksmanship they are much better than airsoft guns and do not require a license of any sort. Some PCPs have excellent bolt-actions, I'd be happy to point you in the right direction if you need help.

If you are after authentic period replicas, I'm working on spring and gas powered Lee-Enfields with a higher level of realism than most China-made models and less... explosive(?) than the Ironairsoft SMLE!