Are opposition planned?
I'd intended to use mine for Borneo, but got a bit of a bollocking from the father-in-law for trying to use figures with their sleeves rolled up. 
You still can. The preponderance of photos from the period shows troops with sleeves rolled. The only, minor issue,is that the figures are wearing boots and putees rather than jungle boots but personally, I've let that slide. I have a platoon in jungle green for Borneo, Brunei,Belize and my fictional Caribbean colony and a platoon in khaki for Aden and Kuwait.
The original figures, could be used for Kenya but only really for the last year/ months of the war.
There's a rumour of a possible Landrover and crew for the Argyles. Personally, I'd love to see a 'Mad Mitch' figure. I'd also like to see one or two figures ore suited to FLOSY ot the NLF, maybe pistol or SMG armed bomb throwers. Hopefullu, there might be some beret wearing variants at some point.
As for opposition, there's a range of tribesmen already available. One or two would make reasonable urban types, especially the Sten gunner. Others can be gleaned from the ZANLA guerillas and some other ranges like Artizan. I've done a small platoon of rebels for the Brunei revolt by converting a variety of figures including a number of Eureka's Vietnam range, their footballers and one or two from the ZANLA range. Traditional SE Asian songkok hats are simply Wargames Factory Russian heads in sidecaps.