There are quite a few 303 doubles around.

Just depends on what you want to spend.

Holland, Rigby made some, I have also seen Andrews.

Mickey has one he bought in Australia - can't remeber the name of the maker.

Build one - I wouldn't bother - buy a 30.06 double or a 9.3 x 74R.
Much more practical, a hell of a lot less hassle and you can have it now instead
of waiting a year !!!

500 Nitro