I've found that at least here in the states, rebuildable originals are not difficult to come by.
Ideally, you want a -1 as your spare, not a -3 - the -1 will work in all games that were made with -1, -3 and -4 boards. The -3 and -4 won't work in a -1 game (basically anything pre-Fliptronics, including t2, funhouse, etc) due to lack of several components that were no longer required after the games started shipping with fliptronics boards.
The rottendog stuff doesn't seem to have a great reputation. Seems there are compatibility issues with some of their boards. I've not heard of any compatibility issues with their driver boards, but I know their CPU won't work in TZ.
