Mikael
Although Franek means just Frank in Polish, it does not mean Frank is me in English (US).
Anyway, if I can add to Frank's comments, I would suggest you to trawl through PRO/NA on line catalogue. I do not know if you are familiar with ORBs but I can imagine you may find them worthy to purchase on microfilm. Thus, I suggest you to check not microfilmed stuff, which is harder to access but still very interesting. In case you will order the microfilm, do not waste time but get through the latter papers.
Staff there is very helpful, so you can always ask there for assistance.
Good luck!