Hi Bill
Someone in Europe makes replacement needles, I forget who, but a bit of Net searching should find them. As regards the front barrel band, keep an eye on the German site "eGun". I have seen at least one lot of brasses go through during the past year. There is even a front end on there now, but sadly it won't fit your M1862, in fact I am not even sure it is for an M1841 as it isn't the same as mine.
Good luck with your search! The Dreyse rifle is a thing of beauty and looks terrific when displayed with a good M1860 helmet. You may have to be patient, but I am sure you will get there in the end.
Some truly magnificent Dreyse rifles on show here:
http://tirmilitaria.heberg-forum.net/ftopic7096_fusil-dreyse.html
Best wishes,
S.
[Add: I cannot send you the M1862 needle dimensions as my M1862 is also missing the needle and I have never bothered to replace it.]