I'm an American living in Italy and not currently in the armed forces. However, when I was on active duty it was typical for military personnel stationed in foreign countries to keep the registration and license plate associated with their home country. Of course this was back during the War of 1812, so things may have changed. But I'll ask the question anyhow.
Are you required to register the car in Germany or can you keep the UK registration because you're in the armed forces ( that's what HM forces means, doesn't it?)
It seems to me that if it's legal for me to drive in the UK with my Italian Alfa by simply moving the headlight beam adjustment lever, it should be legal for you to do the same in Germany.
If you MUST have European specification headlamps, why not buy them on Italian Ebay? Do a search for "faro Alfa 159" on EBay.it and you'll find plenty of them for less than 100€. When you return to the UK you can most likely resell them for the same price.