When most games are delisted they’re simply removed from the public facing marketplaces where you would have bought them. Your previous purchases are usually maintained in a download history or purchase history page. The steps to get to these pages differs by platform and usually changes at least once a year.
To keep things better organized, I’ve made individual pages for each console and platform that I can update more regularly. Take your pick below and get your delisted games back! Sorry, still under construction here!
Xbox 360 – Xbox One
Nintendo Wii – Nintendo Wii U
NIntendo 3DS – Nintendo DS