I am not sure if there are many more mandatory search effects in other colors. You can obviously try to include symmetrical searching in green for lands or similar, but your opponent's can always
opt out of that. This list is missing Maralen, who also forces players to search, but I believe maralen to be too bad to play, because the first player just grabs an answer for Ob, or even worse something to steal it. If you want to go a different path, maybe something with shadowborn apostles to search out Ob in response to something is good fun.