Do a search on eBay for a Chinese seller called "Wehonest". Among their many products, they sell boards with many connections specifically designed to randomize building lights on a train layout. If they are out of stock, you won't see the product listed. But eventually they will put it back up. Unfortunately, wehonest sells ten thousand items and it is tedious to search for anything specific. I looked for this and I couldn't find it easily. Maybe you'll have more luck.