I have no experience with reflectors but I do have experience with ordering "bit parts" from Shimano so may be able to help.
The first step was to go to the Shimano site and find the official distributors for my country (UK). I was quite surprised since I'd never heard of them, but fortunately they had a website etc. (So if you have no joy with the German distributor, you may wish to try the UK distributor).
When I contacted them, these people were happy enough to order the stuff for me, but (a) relatively-speaking they were very expensive, and (b) they took an age to arrive - it was like the distributor had to order them from Japan.
If I tell you that what I had was some SL cleats, and all I wanted was something as simple as some replacement screws (this was when I first started riding, one of mine fell out one day so I figured it would be sensible to get some spares). With hindsight I should have just bought some new cleats, which of course I ended up doing anyway eventually.
Its as few years ago but I can have a look through my old emails and find out exactly who I ordered off, if you can't find this on the Shimano site. Let me know if you'd like me to do this.
Hope this helps some.