Ds1 is getting a bit old for playmobil but is still asking for bits of battle equipment and soldiers. I know he would love toy soldiers (the more numerous the better) together with some bits of kit he could use to set up battle scenes - look out towers, battlements, defences etcc etc. I've tried googling 'toy soldiers' but can't find anything quite right. Does anything like this exist? what about warhammer? is that similar? or is he still a bit young for that? <ignorant emoticon>
I would go into a games workshop if you have one locally. The geeks people who work in there are very knowledgeable and can give great advice to beginners. My DS (7) isn't really interested in the games, but is fascinated by the tween boys who stand by the tables in games workshop enacting scenes with their toolbox style cases alongside.
Don't know if it's exactly what you are looking for or even if it's a bit too young but if you look up World Peacekeeper toys (bit like action man) they have loads of bits to make up battles and stuff.
I was in John Lewis today: they had a box of small khaki ((presumably paintable) plastic soldiers at either £3.99 or £4.99 (sorry, brain has gone a bit soft). There was also a larger tub of Toy Story tie-in ones; dare say you'd be able to find those in a lot of department stores.