In reply to Wilbur: arc'terx do gore tex shelled primaloft belay jackets.
but, why on earth do you need a waterproof belay jacket? you should only be usung it in cold ocnditions where there is little or no water. even if you use it in scotland where it is wet, if you get quality synthetic jacket, it still retains most of its insulating properties when wet. adding a water proof shell to the jacket, reduces its breathablity, making it harder to dry your clothes. it adds weight and builk and unessessary cost. read the chapter in mark twights extreme alpinism on them.
for my money get a micro puff jacktet of DAS parka.