sourcing question 

I've been contacted by the unit historian for 4th Supply Battalion, who has given me some information and an image to use for that article. However, it's not published anywhere but in the unit's records, which are not generally accessable to anyone not at the unit's headquarters. How would I be able to source this information in order to use it in the article? Would I be able to forward the email to OTRS and cite the ticket as a source? Or perhaps simply just cite "unit historian"? It would be a shame to be unable to use this history. Thanks in advance. ''''''wordsdeeds