If you want one now, then the only PAYWARE models I know of are on the UKRailwaves website - http://shop.alphatwofive.com/product_info.php?cPath=25_27&products_id=46 and you have to register first for free before purchasing anything, and you get 3 different liveried locomotives for £6.50, however, they don't have a custom engine sound or an authentic cab interior, but, for the small amount of money, there excellent to drive and look good, and you've got them forever.......
There was talk of a Class 60 being created at the moment to be uploaded to the DLS, but, when that will be finished is anyone's guess, and I am unsure for which version of Trainz it is for. It's up to you whether to hang on for a few weeks/months or get one now......