Back in college, my buddies and I would play some massive tables, with like 8+ people. It took us a while, but we found a few things that worked.
What I'd recommend is:
1 Sheriff, 1 Deputy, 3 Renegades, 4 Outlaws.
New mechanic we made up: "Fog of War". Fog of War is a distance bonus applied to all characters that decreases by 1 at the start of the next round. Its value at the start of the game is simply
(# of Players)-5, with a maximum of 3.
(1) The increased Renegade count is to counteract the fact that Renegades get harder and harder to play as the player count increases. However, up until the last moments of the game, the Renegades all share a similar goal. And, unlike the Deputies, Renegades have the benefit of wanting to kill other targets who might not be you at the end (like the Deputy). As a result, having more Renegades is easier on the Renegade "goal" than having more Deputies.
(2) With 9 players, you'll have 3 rounds of a lull where few shots will be fired and players will be able to get a sense of threats and neighbors. This mostly puts benefit in the Sheriff's favor, to counteract the fact that 44% of the table want him dead from the start, and the rest don't know who to shoot. This also helps mitigate the loss in power against The Law from the reduced number of Deputies from houserule #1.