Hello Phil,
A careful look by a professional researcher in Pietermaritzburg would be needed to see if Kirkwood has left any footprint whatsoever, I certainly was not suggesting merely looking at their site, my own feeling is, as already stated, that he might have been a one time resident of the Colony, as you clearly stated in your original post that he did fight in 1906.
Likewise, any researcher will be able to look at Kew for you, I do not normally use researchers, so I really cannot recommend one above another, however, there are an awful lot of them these days and it is important to choose one who will accept your payment and one who is familiar with the particular War Office file you require, as well as being able to do a fast turn around for you, so many are based within a few minutes walk away and this is an obvious advantage.
WO126 certainly used to be in a very poor state, I well remember looking at the Imperial Light Horse a good few years ago and there were papers that were not where they should have been, as a result, a friend of mine, who did ask a researcher to look for a particular gentleman's paper, was told that it was not present, in many cases, that is indeed true, not all have survived, but, not in this particular case, so again, the importance of choosing well is highlighted, but, upon reading your last post, you are saying the particular papers actually are in WO126, so you do actually know they exist?
The nominal rolls in WO127 are really just that and nothing more, a polite note to David, djb, the administrator on here, should result in complete uncropped photographs being sent to you, rather than just those available.
Regards Frank