The BEF 1940 (although could be used for another 18months) is the obvious choice. Could be used for Battle of France, possibly Norway, home guards, operation Sealion and the AngloFrench force for Finland that was proposed but never took place. With all those excess early German sets available they do need some opposition for the period that France surrendered.
I make up sets of toy soldiers with scenery etc that I give away to families that don't have much. Imaginative play is important for child development and also for adult mental health but pocket money toys are rare, corporates prefer 'merchandising', preferably 'collectable merchandising' so the cost is high the scale is arbitary and the play value is poor at best. The three eras that I get asked for most are 'knights', 'WW2' and 'Sci-Fi' (specifically 'a space base'). The first two are well catered for (although making castles is a pain) but sci-fi is a lot more difficult. At the moment I use DDS Space Battles set 1 (16 figures in 8 poses and two walkers) or modified WW2 US Paratroopers for space troopers and Roman or medieval civilians with some WW2 ground crew for space base personnel. So I would appreciate a toy sent of space troopers and a set of 'space pirates' for the troopers to deal with. Futuristic civilians and maintenance personnel would be nice, As these are for playing with rather than wargaming the number of poses is significant and it would be nice to have no more than two of any one pose (say 20 figures in 10 poses). I don't expect this to happen but I thought I should pass on my own experiences. Kids are supposed to like computer games but the main complaint I got was 'I want my dining table back' so now I supply a 48x18 inch 'battle board'. Thus far over half the kids have taken to it and they will represent the future wargamers
Just like to say I'm a big fan of your models and would like to say thank you. Sadly my local hobby store closed down so it is harder to get hold of your figures. May I suggest the WW1Turk cavalry and flying pig mortors, also byzantines.