In my opinion, the only one you can use are askaris, ruga-ruga and british officers. Askaris and ruga-ruga could be used to represent the few irregular troops used on the german side...and british officers could pass as british officers on campaign. COPPLESTONE WW1 British are OK for the period too.
If you are not a button counter, belgian askaris can pass for belgian askaris of the period.
For the rest, I have used BRIGADE GAMES miniatures as they are compatible in size with FOUNDRY and COPPLESTONE minis.