The Green Howards Regimental Museum is located in Trinity Square, Richmond (North Yorkshire).
The Museum has a website at www.greenhowards.org.uk.
If you can visit the Museum, there are several prime sources of material readily available to help you;-
The Battalion War Diaries
Official History of the Regiment in WW1, "The Green Howards in the Last War" by Colonel Wylly
"Officers of the Green Howards, 1688 - 1931" by M L Ferrar
"The History of the Green Howards" by Geoffrey Powell & John Powell
Copies of "Friends of the Green Howards Regimental Museum" and "The Green Howard" (twice yearly publications)
In addition, the Museum has a research room, where you can use a computer to access the internet.
There is MUCH more material available in the Museum, including its collection and photographic archive.
The Museum will be delighted to try and help you. Please contact them in advance via their website.
Although the Museum can undertake research based on information in their archives, it is essential that you read their guidelines before requesting them to undertake any research on your behalf.